CSS Interview Questions

There are several ways to color shapes (including specifying attributes on the object) using inline CSS, an embedded CSS section, or an external CSS file. Most SVGs you find on the web uses inline CSS, but there are advantages and disadvantages associated with each type.

Basic coloring can be done by setting two attributes on the node: fill and stroke. fill sets the color inside the object and stroke sets the color of the line drawn around the object. You can use the same CSS color naming schemes that you use in HTML, whether that's color names (that is red), RGB values (that is rgb(255,0,0)), Hex values, RGBA values, etc.

<rect
  x="10"
  y="10"
  width="100"
  height="100"
  stroke="blue"
  fill="purple"
  fill-opacity="0.5"
  stroke-opacity="0.8" />

The above fill="purple" is an example of a presentational attribute. Interestingly, and unlike inline styles like style="fill: purple" which also happens to be an attribute, presentational attributes can be overridden by CSS styles defined in a stylesheet. Hence if you did something like svg { fill: blue; } it will override the purple fill that has been defined.

TL;DR

You can manipulate CSS styles using JavaScript by accessing the style property of an HTML element. For example, to change the background color of a div element with the id myDiv, you can use:

document.getElementById('myDiv').style.backgroundColor = 'blue';

You can also add, remove, or toggle CSS classes using the classList property:

document.getElementById('myDiv').classList.add('newClass');
document.getElementById('myDiv').classList.remove('oldClass');
document.getElementById('myDiv').classList.toggle('toggleClass');

Manipulating CSS styles using JavaScript

Accessing and modifying inline styles

You can directly manipulate the inline styles of an HTML element using the style property. This property allows you to set individual CSS properties.

// Select the element
const myDiv = document.getElementById('myDiv');

// Change the background color
myDiv.style.backgroundColor = 'blue';

// Set multiple styles
myDiv.style.width = '100px';
myDiv.style.height = '100px';
myDiv.style.border = '1px solid black';

Using the classList property

The classList property provides methods to add, remove, and toggle CSS classes on an element. This is useful for applying predefined styles from your CSS files.

// Select the element
const myDiv = document.getElementById('myDiv');

// Add a class
myDiv.classList.add('newClass');

// Remove a class
myDiv.classList.remove('oldClass');

// Toggle a class
myDiv.classList.toggle('toggleClass');

Modifying styles using CSS variables

CSS variables (custom properties) can be manipulated using JavaScript. This is particularly useful for theming and dynamic styling.

// Set a CSS variable
document.documentElement.style.setProperty('--main-color', 'blue');

// Get the value of a CSS variable
const mainColor = getComputedStyle(document.documentElement).getPropertyValue(
  '--main-color',
);
console.log(mainColor);

Using external stylesheets

You can also manipulate styles by dynamically adding or removing stylesheets.

// Create a new link element
const link = document.createElement('link');
link.rel = 'stylesheet';
link.href = 'styles.css';

// Append the link element to the head
document.head.appendChild(link);

// Remove the link element
document.head.removeChild(link);

Further reading

• MDN Web Docs: Element.style
• MDN Web Docs: Element.classList
• MDN Web Docs: Using CSS custom properties (variables)
• MDN Web Docs: Document.createElement()

The CSS box model describes the rectangular boxes that are generated for elements in the document tree and laid out according to the visual formatting model. Each box has a content area (e.g. text, an image, etc.) and optional surrounding padding, border, and margin areas.

The CSS box model is responsible for calculating:

• How much space a block element takes up.
• Whether or not borders and/or margins overlap, or collapse.
• A box's dimensions.

Box Model Rules

• The dimensions of a block element are calculated by width, height, paddings, and borders.
• If no height is specified, a block element will be as high as the content it contains, plus padding (unless there are floats, for which, see describe floats and how they work).
• If no width is specified, a non-float-ed block element will expand to fit the width of its parent minus the padding, unless it has a max-width property set, in which case it will be no wider than the specified maximum width.
  • Some block-level elements (e.g. table, figure, and input) have inherent or default width values, and may not expand to fill the full width of their parent container.
  • Note: span is an inline-level element and does not have a default width, so it will not expand to fit.
• The height of an element is calculated by the content's height.
• The width of an element is calculated by the content's width.
• By default (box-sizing: content-box), paddings and borders are not part of the width and height of an element.

Note that margins are not counted towards the actual size of the box. It affects the total space that the box will take up on the page, but only the space outside the box. The box's area stops at the border — it does not extend into the margin.

Extra

Look up the box-sizing property, which affects how the total heights and widths of elements are calculated.

• box-sizing: content-box: This is the default value of box-sizing and adheres to the rules above.

  For example:

  .example {
    box-sizing: content-box;
    width: 100px;
    padding: 10px;
    border: 5px solid black;
  }

  The actual space taken by the .example element will be 130px wide (100px width + 10px left padding + 10px right padding + 5px left border + 5px right border).

• box-sizing: border-box: The width and height will include the content, padding and border (but not the margin). This is a much more intuitive way to think about boxes and hence many CSS frameworks (e.g. Bootstrap, Tailwind, Bulma) set * { box-sizing: border-box; } globally, so that all elements use such a box model by default. See the question on box-sizing: border-box for more information.

  For example:

  .example {
    box-sizing: border-box;
    width: 100px;
    padding: 10px;
    border: 5px solid black;
  }

  The element will still take up 100px on the page, but the content area will be 70px wide (100px - 10px left padding - 10px right padding - 5px left border - 5px right border).

Border and Margin Behavior

• Borders do not collapse or overlap with those of adjacent elements. Each element’s border is rendered individually.
• Margins can collapse, but only vertically and only between block-level elements. Horizontal margins do not collapse. This means that if one block element has a bottom margin and the next has a top margin, only the larger of the two will be used. This behavior is independent of box-sizing and is the default in CSS.

References

• The box model | MDN

* { box-sizing: border-box; } makes every element on the page use the box-sizing: border-box approach for calculating the elements height and width.

What's the difference?

By default, elements have box-sizing: content-box applied, and only the content size is being accounted for if an element has height and width specified. box-sizing: border-box changes how the width and height of elements are being calculated, border and padding are also being included in the calculation. The height of an element is now calculated by the content's height + vertical padding + vertical border width. The width of an element is now calculated by the content's width + horizontal padding + horizontal border width.

The following table indicates whether the property is included in the element's calculation of height and width when it has the respective box-sizing:

Advantages

Taking into account paddings and borders as part of the box model resonates better with how designers actually imagine content in grids. This is a much more intuitive way to think about boxes and hence many CSS frameworks set * { box-sizing: border-box; } globally, so that all elements use such a box model by default.

References

• Box Sizing | CSS-Tricks

The common values for the display property: none, block, inline, inline-block, flex, grid, table, table-row, table-cell, list-item.

For a complete list of values for the display property, refer to CSS Display | MDN.

References

• CSS Display | MDN

A positioned element is an element whose computed position property is either relative, absolute, fixed or sticky.

• static: The default position; the element will flow into the page as it normally would. The top, right, bottom, left and z-index properties do not apply.
• relative: The element's position is adjusted relative to itself, without changing layout (and thus leaving a gap for the element where it would have been had it not been positioned).
• absolute: The element is removed from the flow of the page and positioned at a specified position relative to its closest positioned ancestor if any, or otherwise relative to the initial containing block. Absolutely-positioned boxes can have margins, and they do not collapse with any other margins. These elements do not affect the position of other elements.
• fixed: The element is removed from the flow of the page and positioned at a specified position relative to the viewport and doesn't move when scrolled.
• sticky: Sticky positioning is a hybrid of relative and fixed positioning. The element is treated as relative positioned until it crosses a specified threshold, at which point it is treated as fixed-positioned.

These two approaches are not mutually exclusive. Making a website responsive means that some elements will respond by adapting its size or other functionality according to the device's screen size, typically the viewport width, through CSS media queries, for example, making the font size smaller on smaller devices.

@media (min-width: 768px) {
  .my-class {
    font-size: 24px;
  }
}

@media (max-width: 767px) {
  .my-class {
    font-size: 12px;
  }
}

A mobile-first strategy is also responsive, however it agrees we should default and define all the styles for mobile devices, and only add specific responsive rules to other devices later. Following the previous example:

.my-class {
  font-size: 12px;
}

@media (min-width: 768px) {
  .my-class {
    font-size: 24px;
  }
}

A mobile-first strategy has the following main advantages:

• It's more performant on mobile devices, since all the rules applied for them don't have to be validated against any media queries.
• Mobile-first designs are more likely to be usable on larger devices (will just appear more stretched, but still usable). However, the reverse is not the case.

There are four types of @media properties (including screen):

• all: for all media type devices
• print: for printers
• speech: for screen readers that "reads" the page out loud
• screen: for computer screens, tablets, smart-phones etc.

Here is an example of print media type's usage:

@media print {
  body {
    color: black;
  }
}

Float is a CSS positioning property. Floated elements remain a part of the flow of the page, and will affect the positioning of other elements (e.g. text will flow around floated elements), unlike position: absolute elements, which are removed from the flow of the page.

The CSS clear property can be used to be positioned below left/right/both floated elements.

If a parent element contains nothing but floated elements, its height will be collapsed to nothing. It can be fixed by clearing the float after the floated elements in the container but before the close of the container.

Clearfix hack

The .clearfix hack uses a clever CSS pseudo-element (::after) to clear floats. Rather than setting the overflow on the parent, you apply an additional class clearfix to it. Then apply this CSS:

.clearfix::after {
  content: ' ';
  visibility: hidden;
  display: block;
  height: 0;
  clear: both;
}

Alternatively, give overflow: auto or overflow: hidden property to the parent element which will establish a new block formatting context inside the children and it will expand to contain its children.

Trivia

In the good old days, CSS frameworks such as Bootstrap 2 used the float property to implement its grid system. However with CSS Flexbox and Grid these days, there is no longer much need to use the float property.

References

• Clearfix: A Lesson In Web Development Evolution

A CSS pseudo-element is a keyword added to a selector that lets you style a specific part of the selected element(s). They can be used for decoration (::first-line, ::first-letter) or adding elements to the markup (combined with content: ...) without having to modify the markup (:before, :after).

• ::first-line and ::first-letter can be used to decorate text.
• Used in the .clearfix hack as shown above to add a zero-space element with clear: both.
• Triangular arrows in tooltips use ::before and ::after. Encourages separation of concerns because the triangle is considered part of styling and not really the DOM.

Notes

• Pseudo-elements are different from pseudo-classes, which are used to style an element based on its state (such as :hover, :focus, etc).
• Double colons should be used instead of single colon to distinguish pseudo-classes from pseudo-elements. Most browsers support both syntaxs since this distinction was not clear in legacy W3C specs.

References

• Pseudo-elements - CSS | MDN

Likes

• Mostly the advantages mentioned in "What are the advantages/disadvantages of using CSS preprocessors?".
• Less is written in JavaScript, which plays well with Node.

Dislikes

• Sass relies on node-sass, which is a binding for LibSass written in C++. The library has to be recompiled frequently when switching between Node.js versions.
• In Less, variable names are prefixed with @, which can be confused with native CSS keywords like @media, @import and @font-face rule.

Before Flex became popular (around 2014), the float-based grid system was the most reliable because it still has the most browser support among the alternative existing systems (flex, grid). Bootstrap was using the float approach until Bootstrap 4 which switched to the flex-based approach.

Today, flex is the recommended approach for building grid systems and has decent browser support (99.64%).

For the adventurous, they can look into CSS Grid Layout, which uses the shiny new grid property. Grid is a two-dimensional grid-based layout system as compared to Flexbox, which is one-dimensional.

Flexbox is mainly meant for 1-dimensional layouts while Grid is meant for 2-dimensional layouts.

Flexbox solves many common problems in CSS, such as vertical centering of elements within a container, sticky footer, etc. famous CSS frameworks like Bootstrap and Bulma are based on Flexbox, and Flexbox is still the tested and proven way to create a variety of layouts.

Grid is meant for two-dimensional layouts, giving you full control over both rows and columns. It offers an intuitive and powerful way to create complex grid-based designs directly in CSS, often with less code and more flexibility than older techniques. Browser support for Grid is now strong across all major modern browsers, making it a solid option for layout design in most projects.

An example would be transforming a stacked pill navigation into a fixed-bottom tab navigation beyond a certain breakpoint.

Firstly, understand that browsers match selectors from rightmost (key selector) to left. Browsers filter out elements in the DOM according to the key selector and traverse up its parent elements to determine matches. The shorter the length of the selector chain, the faster the browser can determine if that element matches the selector. Hence avoid key selectors that are tag and universal selectors. They match a large number of elements and browsers will have to do more work in determining if the parents do match.

BEM (Block Element Modifier) methodology recommends that everything has a single class, and, where you need hierarchy, that gets baked into the name of the class as well, this naturally makes the selector efficient and easy to override.

Be aware of which CSS properties trigger reflow, repaint, and compositing. Avoid writing styles that change the layout (trigger reflow) where possible.

Advantages

• CSS is made more maintainable.
• Easier to write nested selectors.
• Variables for consistent theming. Can share theme files across different projects. This is not necessarily useful with CSS custom properties (frequently called CSS variables).
• Mixins to generate repeated CSS.
• Sass and Less have features like loops, lists, and maps can make configuration easier and less verbose.
• Splitting your code into multiple files during development. CSS files can be split up too but doing so will require an HTTP request to download each CSS file.

Disadvantages

• Requires tools for preprocessing. Re-compilation time can be slow.
• Not writing currently and potentially usable CSS. For example, by using something like postcss-loader with webpack, you can write potentially future-compatible CSS, allowing you to use things like CSS variables instead of Sass variables. Thus, you're learning new syntax that could pay off if/when they become standardized.

These techniques are related to accessibility (a11y).

Small/zero size

width: 1px; height: 1px and a combination of using CSS clip to make the element take up (barely any) space on the screen at all.

Using width: 0; height; 0 is not recommended because search engines might penalize this thinking it has a malicious intention, like keyword stuffing.

Absolute positioning

position: absolute; left: -99999px will position an element way outside of the screen. However, as per WebAIM's article:

Navigable elements, such as links and form controls, should not be hidden off-screen. They would still be navigable by sighted keyboard users, but would not be visible to them, unless they are styled to become visible when they receive keyboard focus.

Use this only when your contents contain only text.

Text indentation

text-indent: -9999px. This only works on text within the block elements. Similar to the absolute positioning technique above, focusable elements given this style will still be focusable, causing confusion for sighted users who use keyboard navigation.

Incorrect ways

The following ways are incorrect because they hide content from the user AND screen readers, which is incorrect if the purpose is to expose to screen readers only.

• display: none
• visibility: hidden
• hidden attribute

Techniques in the wild

Ideally, it is recommended to combine the above approaches to make sure it works properly in all browsers.

Instead of implementing your own way to remove an element from the rendering tree and the a11y tree, you are recommended to use one of the following approaches from mature CSS frameworks, which have been battle-tested on many websites.

Tailwind CSS

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

Bootstrap CSS

.visually-hidden,
.visually-hidden-focusable:not(:focus):not(:focus-within) {
  position: absolute !important;
  width: 1px !important;
  height: 1px !important;
  padding: 0 !important;
  margin: -1px !important;
  overflow: hidden !important;
  clip: rect(0, 0, 0, 0) !important;
  white-space: nowrap !important;
  border: 0 !important;
}

References

• CSS in Action - Invisible Content Just for Screen Reader Users

• Empty div method: <div style="clear:both;"></div>.
• Clearfix method: Refer to the .clearfix class above.
• overflow: auto or overflow: hidden method: Parent will establish a new block formatting context and expand to contains its floated children.

In large projects, having a utility .clearfix class will be very helpful. overflow: hidden might clip children if the children is taller than the parent and is not very ideal.

• Bootstrap: Slow release cycle. Bootstrap 4 has been in alpha for almost 2 years. Future versions of Bootstrap should include a spinner button component, as it is widely used.
• Semantic UI: Source code structure makes theme customization extremely hard to understand. Its unconventional theming system is a pain to customize. Hardcoded config path within the vendor library. Not well-designed for overriding variables unlike in Bootstrap.
• Bulma: A lot of non-semantic and superfluous classes and markup required. Not backward-compatible. Upgrading versions breaks the app in subtle manners.

When multiple CSS rules could apply to the same HTML element, the browser needs a way to decide which rule takes precedence. This is determined by the CSS cascade, which considers importance, inline styles, selector specificity, and source order. Selector specificity is a key part of this process, calculating a weight for each selector.

The browser determines what styles to show on an element depending on the specificity of the CSS rules that match it. Specificity is calculated for each rule to decide which one takes precedence.

How is specificity computed?

The specificity algorithm is basically a three-column value of three categories or weights - ID, CLASS, and TYPE - corresponding to the three types of selectors. The value represents the count of selector components in each weight category and is written as ID - CLASS - TYPE. The three columns are created by counting the number of selector components for each selector weight category in the selectors that match the element.

1. ID: This is the count of ID selectors (e.g., #example).
2. CLASS: This is the count of class selectors (e.g., .my-class), attribute selectors (e.g., [type="radio"]), and pseudo-classes (e.g., :hover).
3. TYPE: This is the count of type selectors (element names, e.g., h1, div) and pseudo-elements (e.g., ::before).

When comparing selectors to determine which has the highest specificity, look from left to right (ID, then CLASS, then TYPE), and compare the highest value in each column. A value in the ID column will override values in the CLASS and TYPE columns, no matter how large they are. Similarly, a value in the CLASS column overrides any value in the TYPE column. For example, a specificity of 1,0,0 (one ID) is greater than 0,10,10 (ten classes and ten types).

It's important to remember that specificity is part of the broader CSS cascade. Declarations marked !important have the highest precedence, followed by inline styles (using the style attribute). Selector specificity comes next.

In cases of equal specificity among competing rules (that aren't inline or !important), the rule that appears last in the CSS source order is the one that counts and will be applied.

It's a better practice to write CSS rules with low specificity so that they can be easily overridden if necessary. When writing CSS for UI component libraries, it is important that styles have low specificities so that users of the library can customize them without needing overly complex selectors or resorting to !important.

References

• Specificity | MDN
• Specificity | web.dev

A Block Formatting Context (BFC) is part of the visual CSS rendering of a web page in which block boxes are laid out. Floats, absolutely positioned elements, inline-blocks, table-cells, table-captions, and elements with overflow other than visible (except when that value has been propagated to the viewport) establish new block formatting contexts.

Knowing how to establish a block formatting context is important, because without doing so, the containing box will not contain floated children. This is similar to collapsing margins, but more insidious as you will find entire boxes collapsing in odd ways.

A BFC is an HTML box that satisfies at least one of the following conditions:

• The value of float is not none.
• The value of position is neither static nor relative.
• The value of display is table-cell, table-caption, inline-block, flex, or inline-flex, grid, or inline-grid.
• The value of overflow is not visible.

In a BFC, each box's left outer edge touches the left edge of the containing block (for right-to-left formatting, right edges touch).

Vertical margins between adjacent block-level boxes within the same BFC can collapse, but a BFC prevents margin collapsing with elements outside of it. Read more on collapsing margins.

The z-index property in CSS controls the vertical stacking order of elements that overlap. z-index only affects positioned elements (elements which have a position value which is not static) and its descendants or flex items.

Without any z-index value, elements stack in the order that they appear in the DOM (the lowest one down at the same hierarchy level appears on top). Elements with non-static positioning (and their children) will always appear on top of elements with default static positioning, regardless of the HTML hierarchy.

A stacking context is an element that contains a set of layers. Within a local stacking context, the z-index values of its children are set relative to that element rather than to the document root. Layers outside of that context — i.e. sibling elements of a local stacking context — can't sit between layers within it. If an element B sits on top of element A, a child element of element A, element C, can never be higher than element B even if element C has a higher z-index than element B.

Each stacking context is self-contained - after the element's contents are stacked, the whole element is considered in the stacking order of the parent stacking context. A handful of CSS properties trigger a new stacking context, such as opacity less than 1, filter that is not none, and transform that is notnone.

Note: What exactly qualifies an element to create a stacking context is listed in this long set of rules.

CSS sprites combine multiple images into one single larger image file and uses a combination of CSS background-image, background-position and background-size to select a specific part of the larger image as the desired image.

It used to be a commonly-used technique for icons (e.g. Gmail uses sprites for all their images).

Advantages

• Reduce the number of HTTP requests for multiple images (only one single request is required per spritesheet). But with HTTP2, loading multiple images is no longer much of an issue.
• Advance downloading of assets that won't be downloaded until needed, such as images that only appear upon :hover pseudo-states. Blinking wouldn't be seen.

How to implement

1. Use a sprite generator that packs multiple images into one and generate the appropriate CSS for it.
2. Each image would have a corresponding CSS class with background-image and background-position properties defined.
3. To use that image, add the corresponding class to your element.

The generated stylesheet might look something like:

.icon {
  background-image: url('https://example.com/images/spritesheet.png');
  width: 24px;
  height: 24px;
}

.icon-cart {
  background-position: 0 0;
}

.icon-arrow {
  background-position: -24px 0;
}

And can be used in the HTML as such:

<span class="icon icon-cart"></span>

<span class="icon icon-arrow"></span>

References

• Implementing image sprites in CSS - CSS: Cascading Style Sheets | MDN

This question is related to the question about writing efficient CSS. Browsers match selectors from rightmost (key selector) to the left. Browsers filter out elements in the DOM according to the key selector and traverse up its parent elements to determine matches. The shorter the length of the selector chain, the faster the browser can determine if that element matches the selector.

For example, with a selector p span, browsers firstly find all the <span> elements and traverse up its parent all the way up to the root to find the <p> element. For a particular <span>, as soon as it finds a <p>, it knows that the <span> matches the selector, and can stop traversing its parents.

Retina is just a marketing term to refer to high resolution screens with a pixel ratio bigger than 1. The key thing to know is that using a pixel ratio means these displays are emulating a lower resolution screen in order to show elements with the same size. Nowadays we consider all mobile devices retina defacto displays.

Browsers by default render DOM elements according to the device resolution, except for images.

In order to have crisp, good-looking graphics that make the best of retina displays we need to use high resolution images whenever possible. However using always the highest resolution images will have an impact on performance as more bytes will need to be sent over the wire.

To overcome this problem, we can use responsive images, as specified in HTML5. It requires making available different resolution files of the same image to the browser and let it decide which image is best, using the html attribute srcset and optionally sizes, for instance:

<div responsive-background-image>
  <img
    src="/images/test-1600.jpg"
    sizes="
      (min-width: 768px) 50vw,
      (min-width: 1024px) 66vw,
      100vw"
    srcset="
      /images/test-400.jpg   400w,
      /images/test-800.jpg   800w,
      /images/test-1200.jpg 1200w
    " />
</div>

It is important to note that browsers which don't support HTML5's srcset (i.e. IE11) will ignore it and use src instead. If we really need to support IE11 and we want to provide this feature for performance reasons, we can use a JavaScript polyfill, e.g. Picturefill.

For icons, to use SVGs where possible, as they render very crisply regardless of resolution.

Techniques

• Graceful degradation: The practice of building an application for modern browsers while ensuring it remains functional in older browsers.
• Progressive enhancement: The practice of building an application for a base level of user experience, but adding functional enhancements when a browser supports it.
• Use caniuse.com to check for feature support.
• Autoprefixer for automatic vendor prefix insertion.
• Feature detection using Modernizr.
• Use CSS Feature queries via `@support``

Both responsive and adaptive design attempt to optimize the user experience across different devices, adjusting for different viewport sizes, resolutions, usage contexts, control mechanisms, and so on.

Responsive design works on the principle of flexibility - a single fluid website that can look good on any device. Responsive websites use media queries, flexible grids, and responsive images to create a user experience that flexes and changes based on a multitude of factors. Like a single ball growing or shrinking to fit through several different hoops.

Adaptive design is more like the modern definition of progressive enhancement. Instead of one flexible design, adaptive design detects the device and other features and then provides the appropriate feature and layout based on a predefined set of viewport sizes and other characteristics. The site detects the type of device used and delivers the pre-set layout for that device. Instead of a single ball going through several different-sized hoops, you'd have several different balls to use depending on the hoop size.

Both of these methods have some issues that need to be weighed:

• Responsive design can be quite challenging, as you're essentially using a single albeit responsive layout to fit all situations. How to set the media query breakpoints is one such challenge. Do you use standardized breakpoint values? Or, do you use breakpoints that make sense to your particular layout? What if that layout changes?
• Adaptive design generally requires user agent sniffing, or DPI detection, etc., all of which can prove unreliable.

• After identifying the issue and the offending browser, use a separate style sheet that only loads when that specific browser is being used. This technique requires server-side rendering though.
• Use libraries like Bootstrap that already handles these styling issues for you.
• Use autoprefixer to automatically add vendor prefixes to your code.
• Use Reset CSS or Normalize.css.
• If you're using PostCSS (or a similar CSS transpilation library), there may be plugins which allow you to opt in to using modern CSS syntax (and even W3C proposals) that will transform those sections of your code into equivalent backward-compatible code that will work in the targets you've used.

translate() is a possible value of the CSS transform property. When using translate(), the element still occupies its original space (sort of like position: relative). But when changing the absolute positioning of elements, the elements are removed from the flow of the page and the positioning of the surrounding elements will be affected. Hence the page layout will have to be recalculated.

Changing transform or opacity does not trigger browser reflows or repaints but does trigger compositions; On the other hand, changing the absolute positioning triggers reflow. transform causes the browser to create a GPU layer for the element but changing absolute positioning properties uses the CPU. Hence translate() is more efficient and will result in shorter paint times for smoother animations.

Which to choose and why?

Choose resetting when you need to have a very customized or unconventional site design such that you need to do a lot of your own styling and do not need any default styling to be preserved.