50 Most Asked CSS Interview Questions and Answers

Cascading Style Sheets (CSS) is an essential tool for any web developer, allowing you to control the visual presentation of web pages. Whether you're a seasoned developer or just starting, mastering CSS is key to delivering responsive, visually appealing, and user-friendly websites. In this article, we’ll cover the 50 most frequently asked CSS interview questions, along with their answers, to help you ace your next job interview.

50 Most Asked CSS Interview Questions and Answers

1. What is CSS?
Answer: CSS stands for Cascading Style Sheets. It is a stylesheet language used to describe the presentation of HTML elements on a webpage, including layout, colors, fonts, and spacing.

2. What is the difference between class and id selectors in CSS?
Answer:

• class: Can be used multiple times on different elements in an HTML document. Example: .example { color: blue; }.
• id: Must be unique and used only once per document. Example: #example { color: red; }.

3. What is the box model in CSS?
Answer: The CSS box model is a concept that defines how elements are structured and how their dimensions (width, height, padding, border, margin) are calculated. It consists of:

• Content: The actual content area (width and height).
• Padding: Space between the content and the border.
• Border: A line surrounding the padding and content.
• Margin: Space outside the border.

4. What are pseudo-classes in CSS?
Answer: Pseudo-classes are used to define the special state of an element. Examples include :hover, :focus, and :nth-child.
Example: a:hover { color: red; } changes the link color when hovered.

5. How do you center an element horizontally in CSS?
Answer: For block elements, you can use margin: 0 auto; along with a defined width.
Example:

div {
  width: 50%;
  margin: 0 auto;
}

6. What is Flexbox in CSS?
Answer: Flexbox is a CSS layout module designed to provide a more efficient way to align and distribute space among items in a container. It is particularly useful for responsive layouts.
Example:

.container {
  display: flex;
  justify-content: center;
  align-items: center;
}

7. What are CSS Grid and its advantages?
Answer: CSS Grid is a layout system that allows for the creation of complex, grid-based layouts easily. It provides two-dimensional layout control (both rows and columns), which Flexbox does not.
Example:

.container {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  grid-gap: 10px;
}

8. What is the difference between absolute, relative, and fixed positioning in CSS?
Answer:

• absolute: Positioned relative to its nearest positioned ancestor.
• relative: Positioned relative to its normal position in the document flow.
• fixed: Positioned relative to the browser window and does not move even when the page is scrolled.

9. What is the z-index in CSS?
Answer: The z-index property specifies the stack order of elements. Higher z-index values bring the element to the front, while lower values place it behind others. It only works on positioned elements (i.e., position: relative, absolute, or fixed).

10. What is a media query in CSS?
Answer: Media queries are used to apply different CSS rules depending on the screen size or other media types. They are critical for responsive design.
Example:

@media screen and (max-width: 600px) {
  body {
    background-color: lightblue;
  }
}

11. What is the difference between inline, block, and inline-block elements in CSS?
Answer:

• inline: Elements do not start on a new line and only take up as much width as needed. Example: <span>.
• block: Elements start on a new line and take up the full width available. Example: <div>.
• inline-block: Behaves like an inline element but allows setting width and height.

12. How can you apply CSS styles to a specific element without using class or id?
Answer: You can use attribute selectors. For example, to style an element with a specific attribute, you can use:

input[type="text"] {
  background-color: yellow;
}

13. What is the float property in CSS?
Answer: The float property is used to align elements to the left or right within a container, allowing text and inline elements to wrap around it.
Example:

img {
  float: left;
  margin-right: 10px;
}

14. How do you clear floats in CSS?
Answer: You can clear floated elements by using the clear property or by adding a clearfix.
Example:

.clearfix::after {
  content: "";
  display: table;
  clear: both;
}

15. What are em and rem units in CSS?
Answer:

• em: Relative to the font size of the parent element. If the parent has a font size of 16px, 1em = 16px.
• rem: Relative to the root (html) font size. If the root font size is 16px, 1rem = 16px.

16. What is the display property in CSS?
Answer: The display property specifies the display behavior of an element. Common values include:

• block: Displays the element as a block (takes up the full width).
• inline: Displays the element as an inline element.
• flex: Makes the element a flex container.
• grid: Makes the element a grid container.

17. How do you make a background image cover the entire viewport?
Answer: Use background-size: cover; to ensure the background image covers the entire element.

body {
  background-image: url('image.jpg');
  background-size: cover;
  background-position: center;
}

18. What is the position: sticky; property in CSS?
Answer: sticky positioning allows an element to toggle between relative and fixed depending on the user's scroll position. An element with position: sticky; stays fixed once it reaches a specified scroll position.

19. What is the visibility property in CSS?
Answer: The visibility property determines whether an element is visible or hidden without affecting the layout. visibility: hidden; hides the element but still takes up space in the layout, unlike display: none;.

20. What is the transition property in CSS?
Answer: The transition property allows you to create smooth transitions when an element changes from one style to another.
Example:

button {
  transition: background-color 0.3s ease;
}

button:hover {
  background-color: blue;
}

21. How can you create a CSS animation?
Answer: CSS animations can be created using @keyframes to define the animation steps and animation property to apply the animation.
Example:

@keyframes slide {
  from { left: 0; }
  to { left: 100px; }
}

div {
  position: relative;
  animation: slide 2s ease-in-out;
}

22. What is the difference between @import and <link> in CSS?
Answer:

• <link>: External CSS files are linked using the <link> tag, and they load faster as it allows parallel downloads.
• @import: CSS can also be imported using @import, but it results in slower performance because styles are loaded sequentially.

23. What is the calc() function in CSS?
Answer: calc() is a CSS function that allows you to perform calculations to set CSS property values.
Example:

div {
  width: calc(100% - 50px);
}

24. What is inherit in CSS?
Answer: The inherit keyword forces an element to inherit the value of a property from its parent element. For example:

p {
  color: inherit;
}

25. What are the advantages of using CSS preprocessors like SASS or LESS?
Answer: CSS preprocessors provide features like variables, nesting, functions, and mixins, which make writing and managing complex stylesheets easier and more maintainable.

26. What is the outline property in CSS?
Answer: The outline property is similar to border, but it doesn’t take up space and is drawn outside the element’s border. It is often used for accessibility to highlight focused elements.

27. How can you create a full-screen layout in CSS?
Answer: To create a full-screen layout, you can set the height and width of an element to 100% of the viewport size using height: 100vh; and width: 100vw;.

28. What are CSS variables and how do you define them?
Answer: CSS variables, also known as custom properties, allow you to define reusable values across your CSS.
Example:

:root {
  --primary-color: blue;
}

h1 {
  color: var(--primary-color);
}

29. What is the difference between visibility: hidden; and display: none;?
Answer:

• visibility: hidden;: Hides the element but still takes up space in the layout.
• display: none;: Hides the element and removes it from the layout, so it does not take up any space.

30. How do you apply styles to specific child elements using CSS?
Answer: You can use the :nth-child() pseudo-class to style specific child elements.
Example:

li:nth-child(odd) {  background-color: lightgray;}

31. What is the box-sizing property in CSS?
Answer: The box-sizing property defines how the width and height of an element are calculated. By default, the width and height are calculated based on the content-box (excluding padding and border). However, with box-sizing: border-box;, padding and borders are included in the width and height.
Example:

div {
  box-sizing: border-box;
}

32. How can you make a responsive layout in CSS?
Answer: A responsive layout can be achieved using media queries, flexible grid systems (like Flexbox and Grid), and relative units (like %, vw, vh, em, rem).
Example:

@media (max-width: 768px) {
  .container {
    flex-direction: column;
  }
}

33. What is the clip-path property in CSS?
Answer: The clip-path property is used to create clipping masks, which define the visible area of an element. You can create shapes like circles, polygons, or complex paths to hide parts of an element.
Example:

div {
  clip-path: circle(50%);
}

34. How do you create a sticky footer using CSS?
Answer: To create a sticky footer that stays at the bottom of the viewport even if the content is smaller than the page, use the following CSS:

html, body {
  height: 100%;
}
.container {
  min-height: 100%;
  display: flex;
  flex-direction: column;
}
.footer {
  margin-top: auto;
}

35. What is the difference between align-items and align-content in Flexbox?
Answer:

• align-items: Aligns flex items along the cross axis (vertical axis by default) within the flex container.
• align-content: Aligns multiple lines of flex items when there’s extra space in the flex container (applies only to multi-line flex containers).

36. How can you create a responsive image in CSS?
Answer: A responsive image scales to fit its container by using max-width: 100%; and height: auto;. This ensures the image maintains its aspect ratio.

img {
  max-width: 100%;
  height: auto;
}

37. What is the difference between @media and @supports in CSS?
Answer:

• @media: Used to apply CSS rules based on the characteristics of the user’s device, such as screen width or resolution.
• @supports: Used to apply CSS rules only if the browser supports a specific CSS feature.
  Example:

@supports (display: grid) {
  div {
    display: grid;
  }
}

38. What is overflow in CSS, and what are its possible values?
Answer: The overflow property controls how content that exceeds the size of an element’s box is handled.

• visible: Content overflows the box (default).
• hidden: Overflowing content is clipped and not visible.
• scroll: Adds scroll bars to view overflowing content.
• auto: Scroll bars appear only when necessary.

39. How do you vertically align text in a div using CSS?
Answer: You can vertically align text inside a div by using Flexbox or line-height if the div has a fixed height.
Example with Flexbox:

div {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 200px;
}

40. What is the difference between :nth-child() and :nth-of-type() in CSS?
Answer:

• :nth-child(): Selects the nth child element of a parent, regardless of the element type.
• :nth-of-type(): Selects the nth child element of a specific type (e.g., p, div) among its siblings.

41. What is the object-fit property in CSS?
Answer: The object-fit property defines how an image or video is resized to fit within its container.
Common values:

• contain: Scales the content to fit inside the container, maintaining aspect ratio.
• cover: Scales the content to cover the entire container, potentially cropping it.

Example:

img {
  object-fit: cover;
}

42. What are transitions and how do they differ from animations in CSS?
Answer:

• Transitions: Allow changes to CSS properties over a specified duration when triggered by a user action, such as hover or focus.
• Animations: Define a sequence of keyframes that run continuously or based on specific conditions. They provide more control compared to transitions.

Example transition:

button {
  transition: background-color 0.3s;
}

button:hover {
  background-color: blue;
}

43. What is a CSS preprocessor?
Answer: A CSS preprocessor like SASS or LESS adds programming features (variables, nesting, mixins, functions) to CSS, making it easier to write and maintain complex stylesheets. Preprocessors need to be compiled into standard CSS before being used in the browser.

44. How do you create a circular image in CSS?
Answer: You can make an image circular by setting border-radius: 50%; and ensuring the width and height are equal.

img {
  width: 100px;
  height: 100px;
  border-radius: 50%;
}

45. What is the difference between opacity and visibility in CSS?
Answer:

• opacity: Controls the transparency of an element. opacity: 0; makes the element fully transparent, but it still occupies space in the layout.
• visibility: Controls whether the element is visible or hidden. visibility: hidden; makes the element invisible but retains its space in the layout, whereas display: none; removes the element from the layout entirely.

46. What is the backface-visibility property in CSS?
Answer: The backface-visibility property defines whether the backside of an element is visible when it is rotated. This is typically used in 3D transformations.
Example:

div {
  transform: rotateY(180deg);
  backface-visibility: hidden;
}

47. How do you implement a dark mode in CSS?
Answer: Dark mode can be achieved using media queries to detect the user’s system preference for dark or light mode.

@media (prefers-color-scheme: dark) {
  body {
    background-color: black;
    color: white;
  }
}

48. What is a CSS combinator?
Answer: A CSS combinator describes the relationship between two selectors. The four combinators are:

• Descendant (A B): Selects all B elements inside A.
• Child (A > B): Selects all B elements that are direct children of A.
• Adjacent sibling (A + B): Selects the B element that is immediately preceded by A.
• General sibling (A ~ B): Selects all B elements preceded by A.

49. How do you optimize CSS for performance?
Answer:

• Use shorthand properties to reduce code size.
• Minify CSS files to remove unnecessary whitespace and comments.
• Use external stylesheets and cache them for faster load times.
• Avoid excessive use of complex selectors.
• Reduce the number of HTTP requests by combining CSS files.

50. How do you target the first and last child of an element in CSS?
Answer:

• To target the first child, use :first-child.
• To target the last child, use :last-child.
  Example:

li:first-child {  color: red;}li:last-child {  color: blue;}

Conclusion

CSS is a crucial skill for any front-end developer, as it plays a pivotal role in how websites look and feel. Mastering CSS interview questions will not only help you prepare for your job search but also sharpen your skills for real-world projects. Whether you're focusing on the basics or diving deep into advanced concepts like Flexbox and CSS Grid, these questions will give you a strong foundation for your next interview. Good luck!