30 CSS Interview Questions & Answers

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30 CSS Interview Questions & Answers

CSS (Cascading Style Sheets) is an integral part of modern web development, responsible for the visual presentation and layout of web pages. Aspiring web developers, designers, or even experienced professionals often face CSS-related challenges during job interviews. The ability to navigate through CSS intricacies and demonstrate a solid understanding of its concepts is crucial for success in these interviews. This article delves into CSS interview questions and answers, unlocking the secrets to help you ace your next CSS-focused interview. 

Basic-level CSS interview questions

Here are ten basic-level CSS interview questions and their answers:

  • What is CSS?

CSS stands for Cascading Style Sheets. It is a style sheet language used to describe the look and formatting of a document written in HTML or XML.

  • How do you include CSS in a webpage?

CSS can be included in a webpage by using the <link> element in the HTML <head> section or by using the style attribute directly within HTML elements.

  • What is the difference between inline, internal, and external CSS?

Inline CSS is applied directly within HTML elements using the style attribute. Internal CSS is defined within the <style> tags in the HTML <head> section. External CSS is stored in separate CSS files and linked to the HTML document using the <link> element.

  • What are CSS selectors?

CSS selectors are patterns used to select and style specific elements in an HTML document. Examples of selectors include element selectors (p, div), class selectors (.my-class) and ID selectors (#my-id).

  • How can you select elements based on their class and ID?

To select elements based on class, you prefix the class name with a dot (.) such as .my-class. To select elements based on ID, you prefix the ID name with a hash (#) such as #my-id.

  • How do you change the colour of text using CSS?

You can change the colour of text using the colour property in CSS. For example, colour: red; will make the text red.

  • What is the box model in CSS?

The box model is a concept in CSS that defines how elements are displayed and structured. It consists of content, padding, border and margin. These components determine the total size and spacing of an element.

  • How can you centre align an element horizontally and vertically?

To centre align an element horizontally, you can use margin: 0 auto; along with a defined width. To centre align an element vertically, you can use display: flex; along with align-items: centre; within a container.

  • What is a CSS pseudo-class?

A CSS pseudo-class is a keyword that selects specific states or elements in a document. Examples include :hover (when the mouse hovers over an element) and :nth-child(n) (selects the nth child of a parent element).

  • How do you apply CSS to only specific browser versions?

CSS vendor prefixes can be used to apply specific CSS rules to specific browser versions. For example, -webkit- is used for WebKit-based browsers like Chrome and Safari while -moz- is used for Firefox.

Intermediate-level CSS interview questions

Here are ten intermediate-level CSS interview questions and their answers:

  • What is the CSS box-sizing property, and how does it work?

The box-sizing property controls how the width and height of an element are calculated. The default value is content-box, where the width and height do not include padding and border. Setting it to border-box includes padding and border within the specified width and height.

  • What are CSS media queries, and how are they used?

CSS media queries allow you to apply different styles based on the device’s or viewport’s characteristics. By using media query expressions, you can target specific screen sizes, resolutions, orientations and more to create responsive designs.

  • What is the difference between display: inline and display: inline-block?

The display: inline property makes an element behave like an inline element, allowing other elements to appear beside it on the same line. display: inline-block also allows elements to appear inline, but it retains block-level properties such as setting width and height.

  • How can you create a responsive website using CSS?

Responsive web design can be achieved by using CSS media queries, fluid layouts (using percentages or relative units like em or rem), flexible images (max-width: 100%;) and adjusting the design based on the viewport size.

  • What is the CSS float property used for?

The float property allows an element to be taken out of the normal document flow and positioned to the left or right of its containing element. It is commonly used for creating multi-column layouts or floating images within text.

  • How can you vertically align text within an element?

You can vertically align text using the vertical-align property. However, it only applies to inline or table-cell elements. For block-level elements, you can use CSS flexbox or CSS grid to achieve vertical alignment.

  • What is the CSS z-index property, and how does it work?

The z-index property specifies the stacking order of elements along the z-axis (depth). Elements with a higher z-index value will appear above elements with a lower value. It applies to positioned elements (those with a position other than static).

  • What is the purpose of the CSS transform property?

The transform property allows you to apply various transformations to elements, such as rotation, scaling, skewing, and translating (moving). It is useful for creating visually dynamic effects and animations.

  • How can you create a CSS gradient background?

CSS gradients can be created using the linear-gradient() or radial-gradient() functions. These functions allow you to specify the starting and ending colours as well as the direction or shape of the gradient.

  • What is the CSS transition property used for?

The transition property enables you to create smooth transitions between different CSS property values over a specified duration. It is commonly used for animating changes in size, position, colour or other properties of an element.

Advanced-level CSS interview questions

Here are ten advanced-level CSS interview questions and their answers:

  • What are CSS preprocessors, and why are they useful?

CSS preprocessors like Sass, Less, and Stylus are extensions of CSS that provide additional features such as variables, mixins, nesting and functions. They enhance code organisation, and reusability, and make it easier to maintain large CSS codebases.

  • Describe the idea of CSS specificity and how it works.

When numerous rules are directed at the same element, the CSS specificity decides which rule will take precedence. Based on the mix of selectors a rule uses, it is calculated. The specificity value increases with selector specificity (IDs are more particular than classes or tags).

  • What is the CSS grid layout system, and how does it differ from flexbox?

The CSS grid layout system is a two-dimensional layout model that allows you to create complex grid-based designs. It provides precise control over rows and columns. In contrast, flexbox is a one-dimensional layout model used for arranging elements in a row or column, offering flexibility in distribution and alignment.

  • How can you achieve a responsive design without using media queries?

CSS frameworks like Bootstrap or Foundation can provide responsive grids and components that adjust automatically based on the viewport size. Alternatively using CSS Grid or Flexbox and relative units (like percentages or fr units) can create responsive layouts without explicit media queries.

  • What are CSS pseudo-elements? Provide examples.

CSS pseudo-elements are used to style specific parts of an element, such as the first letter or line. Examples include ::before and ::after, which allow you to insert content before or after an element’s content, and ::first-line, which targets the first line of a block-level element.

  • How does CSS animation work, and what are the different animation-related properties?

CSS animation allows you to animate elements without the need for JavaScript. The animation property specifies the animation’s keyframes, duration, timing function, delay, and iteration count. Other animation-related properties include @keyframes, animation-timing-function, animation-delay, and animation-iteration-count.

  • What is the CSS @media rule, and how is it used?

The @media rule is used to apply specific CSS rules based on the characteristics of the output device. It allows you to define different styles for different media types (e.g., screen, print) or specific features (e.g., high-resolution screens).

  • How can you optimise CSS for performance and loading speed?

CSS optimization techniques include minimising and combining CSS files, using CSS minification tools, reducing the number of HTTP requests by avoiding excessive CSS files, and using appropriate selectors to minimise specificity and improve rendering performance.

  • Explain the concept of CSS specificity wars and how to avoid them.

CSS specificity wars occur when conflicting CSS rules result in unintended styles being applied. To avoid them, it’s important to keep CSS selectors simple, avoid excessive use of !important, favour class selectors over IDs, and use CSS methodologies like BEM (Block-Element-Modifier) or OOCSS (Object-Oriented CSS).

  • What are CSS custom properties (variables), and how do they differ from preprocessor variables?

CSS custom properties, also known as CSS variables, allow you to define reusable values that can be used throughout your CSS. Unlike preprocessor variables CSS variables are resolved at runtime by the browser.

Conclusion

This article has explored various CSS interview questions and provided answers to basic, intermediate, and advanced-level inquiries. While this article provides a solid foundation, CSS is an ever-evolving field, and continuous learning is key to staying ahead. Practice implementing CSS concepts in real-world scenarios, explore new features, and stay updated with the latest trends and best practices.

Learn CSS basics for free

If you want to learn some of the basics of CSS for free, try our 5 Day Coding Challenge. After an hour a day over five days, you will learn the basics of HTML, CSS and JavaScript. Register now through the form below. 

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