7 CSS Interview Questions Every Hiring Manager Should Ask

css interview questions

Introduction

CSS (Cascading Style Sheets) plays an important role in contemporary web development, shaping the aesthetic and functional aspects of the web. It’s crucial in current trends like responsive design, animations, and interactive user interfaces, making websites visually appealing and user-friendly across various devices. According to W3Techs, CSS is used by 97.1% of all the websites worldwide. This statistic shows the necessity for developers to have a solid grasp of CSS to create visually appealing and responsive websites.

As CSS continues to evolve with advancements like CSS3, its importance only grows, making proficiency in CSS a key skill for software developers, particularly those focusing on front-end development.

For software engineers specializing in front-end development, proficiency in CSS is essential. It enables them to create seamless experiences, aligning with both design principles and technical performance. 

The purpose of this article is to equip hiring managers with a toolkit of effective CSS interview questions. These CSS interview questions are designed to test a candidate’s technical knowledge, practical skills, problem-solving abilities, and creativity in using CSS.

What is CSS?

CSS, which stands for Cascading Style Sheets, is a technology of the World Wide Web, alongside HTML and JavaScript. It is used to design and layout web pages, controlling the presentation aspect of web development. While HTML is responsible for a web page’s structure and content, CSS defines its look and feel.

The term cascading in CSS refers to the way styles are applied in layers, with multiple style sheets influencing the appearance of a document. CSS rules set in one style sheet can be overridden by rules in another, allowing for a flexible and efficient design process.

According to Statista, CSS is the 2nd (52.57%) most used programming language among developers worldwide as of 2024. This statistic highlights the widespread adoption and significance of CSS in the field of web development.

Key Features of CSS

  1. Separation of Content from Presentation: CSS allows web developers to separate the content of their site (written in HTML) from its visual design. This separation makes it easier to maintain and update the website’s look without changing its content.
  2. Responsive Design: With CSS, developers can create responsive websites that adapt and rearrange their layout to look good on screens of all sizes, from desktop monitors to mobile phones.
  3. Enhanced User Experience: CSS is used to improve the user experience with visual enhancements, animations, transitions, and other dynamic styling features, making websites more engaging and interactive.
  4. Efficiency and Consistency: CSS enables the consistent application of styling across multiple pages of a website. This means that a single change in a CSS file can alter the appearance of multiple pages, making it efficient to manage large websites.
  5. Advanced Styling Capabilities: Beyond basic fonts and colors, CSS offers capabilities like grid and flexbox layouts, custom animations, and the ability to define styles that react to user interactions.

Many top-tier companies across various industries use CSS for web development due to its essential role in creating and styling websites. 

According to W3Techs, some well-known companies include:

  1. Google: Google uses CSS extensively for styling across its various web services and applications.
  2. Facebook: The social media giant relies on CSS for the design and layout of its platform.
  3. Amazon: Amazon’s e-commerce platform utilizes CSS to enhance user experience and interface design.
  4. Twitter: CSS is a key component in styling the user interface of Twitter’s web presence.
  5. Microsoft: Microsoft employs CSS in its web applications and services for layout and styling purposes.

Top 7 CSS Interview Questions

Let’s explore the top 7 CSS interview questions:

1. Implementing a Class for CSS Colors

Task Develop a JavaScript class named CSSColor to represent a CSS color. The class should have a constructor accepting three parameters (red, green, blue) and a method toCSS() for returning the color in CSS format.
Input Format Three integers as input to the constructor, each representing the red, green, and blue components of the color. The toCSS() method requires no arguments.
Constraints
  • The red, green, and blue values are integers.
  • Each color component value ranges from 0 to 255, inclusive.
Output Format The toCSS() method outputs a string in CSS rgb format.
Sample Input let color = new CSSColor(255, 0, 0);
Sample Output console.log(color.toCSS()); // “rgb(255, 0, 0)

Suggested Answer

class CSSColor {

    constructor(red, green, blue) {

        this.red = red;

        this.green = green;

        this.blue = blue;

    }

    toCSS() {

        return `rgb(${this.red}, ${this.green}, ${this.blue})`;

    }

}

Code Explanation

The CSSColor class includes a constructor that initializes the red, green, and blue properties based on the provided arguments. The toCSS() method formats these properties into a CSS rgb string.

Common Mistakes to Watch Out For
  • Not validating the input values to ensure they are within the 0-255 range.
  • Incorrectly formatting the output string in toCSS() method.
Follow-ups
  • How would you extend this class to support RGBA format?
  • Can you implement a method to lighten or darken the color?
What the Question Tests
  • Understanding of CSS color properties.
  • Ability to apply object-oriented programming concepts in JavaScript.
  • Skill in creating a class that models a real-world concept with practical utility.

This question effectively evaluates a developer’s grasp of both CSS and JavaScript, particularly their ability to intertwine styling with programming logic. It’s an excellent way to assess a candidate’s proficiency in front-end development skills.

2. Implementing a Function to Apply CSS Styles

Task Create a JavaScript function applyStyles that takes a CSS selector and a style object as inputs and applies the styles to all elements matching the selector.
Input Format Two arguments: a string for the CSS selector and an object where keys are CSS properties and values are the corresponding styles.
Constraints
  • The CSS selector must be a valid string selector.
  • The style object should contain at least one property-value pair.
Output Format The function does not return a value but modifies the styles of HTML elements.
Sample Input applyStyles(‘p’, { color: ‘red’, fontWeight: ‘bold’ });

Suggested Answer

function applyStyles(selector, styles) {

    let elements = document.querySelectorAll(selector);

    for (let i = 0; i < elements.length; i++) {

        for (let style in styles) {

            elements[i].style[style] = styles[style];

        }

    }

}

Code Explanation

The applyStyles function uses querySelectorAll to select all elements matching the provided selector. It iterates through these elements and, for each element, iterates over each property in the styles object, applying the style to the element’s style object.

Common Mistakes to Watch Out For
  • Forgetting to handle the case when no elements match the selector.
  • Not correctly mapping JavaScript style object properties to CSS properties (e.g., fontWeight in JavaScript vs font-weight in CSS).
Follow-ups
  • How would you modify this function to add !important to all styles?
  • Can this function be optimized for better performance?
What the Question Tests
  • Understanding of manipulating the Document Object Model (DOM) using JavaScript.
  • Knowledge of applying CSS styles through JavaScript.
  • Familiarity with JavaScript functions and loops.

This question is excellent for assessing a candidate’s ability to integrate JavaScript and CSS, a key skill in front-end web development. It tests the practical application of DOM manipulation, a fundamental concept for creating dynamic and interactive web pages.

3. Implementing a Function to Rotate an Element

Task Develop a JavaScript function, rotateElement, that rotates an HTML element to a specified angle. The function takes the element’s id and the rotation angle as inputs.
Input Format Two arguments: a string for the HTML element’s id and a number for the rotation angle in degrees.
Constraints
  • The id must correspond to an existing HTML element.
  • The rotation angle should be a valid number.
Output Format The function modifies the specified element’s style to apply the rotation but does not return a value.
Sample Input rotateElement(‘myDiv’, 45);

Suggested Answer

function rotateElement(id, angle) {

    let element = document.getElementById(id);

    element.style.transform = `rotate(${angle}deg)`;

}

Code Explanation

The rotateElement function locates the HTML element using getElementById and applies a CSS transformation. It sets the element’s transform style to rotate(${angle}deg), effectively rotating the element by the specified angle.

Common Mistakes to Watch Out For
  • Not checking if the element exists before applying the transformation.
  • Confusion between rotation degrees and other units (e.g., radians).
Follow-ups
  • How can this function be adapted to include smooth transition animations?
  • What other transformations could be combined with rotation?
What the Question Tests
  • Familiarity with CSS transformations, particularly rotation.
  • Ability to manipulate HTML elements using JavaScript.
  • Understanding how CSS and JavaScript can be used together to create dynamic effects.

This question effectively evaluates a developer’s skills in both CSS and JavaScript. It tests their ability to use CSS transformations, an important aspect of creating engaging and interactive web interfaces. The task also emphasizes the practical application of JavaScript for DOM manipulation.

4. Implementing a Function to Create a Grid Layout

Task Create a JavaScript function, createGrid, that generates a grid of div elements. The function should accept two arguments representing the number of rows and columns and use a CSS grid layout to arrange these divs.
Input Format Two arguments: positive integers for the number of rows and columns.
Constraints
  • Both rows and columns must be positive integers.
Output Format The function returns a div element styled as a grid with the specified number of rows and columns.
Sample Input let grid = createGrid(3, 3);

Suggested Answer

function createGrid(rows, columns) {

    let grid = document.createElement(‘div’);

    grid.style.display = ‘grid’;

    grid.style.gridTemplateRows = `repeat(${rows}, 1fr)`;

    grid.style.gridTemplateColumns = `repeat(${columns}, 1fr)`;

    for (let i = 0; i < rows * columns; i++) {

        let cell = document.createElement(‘div’);

        cell.textContent = `Cell ${i + 1}`;

        grid.appendChild(cell);

    }

    return grid;

}

Code Explanation

The createGrid function starts by creating a div element and setting its display to ‘grid’. It then defines the grid’s structure using gridTemplateRows and gridTemplateColumns. The function iterates over the total number of cells (rows * columns), creating individual div elements for each cell, setting their text content, and appending them to the grid container. The repeat function in CSS is used to distribute rows and columns evenly.

Common Mistakes to Watch Out For
  • Not setting the correct grid layout properties can lead to an incorrect structure.
  • Forgetting to add each cell to the grid container.
  • Overlooking the need to handle large numbers of rows and columns efficiently.
Follow-ups
  • How would you modify the function to allow different sizes for rows and columns?
  • Could you add functionality to handle grid-gap or cell styling?
What the Question Tests
  • Knowledge of the CSS grid layout, an essential skill for creating responsive designs.
  • Ability to dynamically generate and manipulate HTML elements using JavaScript.
  • Understanding of combining JavaScript and CSS to create complex web layouts.

This question is particularly relevant for front-end development roles, where creating responsive and aesthetically pleasing layouts is a common task. It tests a blend of JavaScript and CSS skills, focusing on dynamic element creation and advanced CSS styling.

5. Implementing a Function for Responsive Design

Task Create a JavaScript function, createResponsiveDiv, that generates a div element. This div should change its width based on the browser window’s width: 100% width for windows less than 600px wide and 50% width otherwise.
Input Format The function takes no arguments.
Constraints
  • The browser window’s width is assumed to be a positive number.
Output Format The function returns an HTML div element styled for responsive design.
Sample Input let responsiveDiv = createResponsiveDiv();

Suggested Answer

function createResponsiveDiv() {

    let div = document.createElement(‘div’);

    let style = document.createElement(‘style’);

    style.innerHTML = `

        #responsiveDiv {

            width: 100%;

        }

        @media (min-width: 600px) {

            #responsiveDiv {

                width: 50%;

            }

        }

    `;

    document.head.appendChild(style);

    div.id = “responsiveDiv”;

    return div;

}

Code Explanation

The createResponsiveDiv function creates a new div and a style element. The style element’s inner HTML sets up CSS rules: initially, the div’s width is set to 100%. A media query is then used to modify this width to 50% for viewport widths of 600px and above. This style element is appended to the document’s head. 

The function assigns the id responsiveDiv to the div and returns it. The CSS within the style tag ensures that the div responds to changes in the viewport width, adhering to the responsive design principles.

Common Mistakes to Watch Out For
  • Forgetting to append the style element to the document would result in the styles not being applied.
  • Incorrectly setting up the media query leads to improper responsive behavior.
  • Not considering other CSS properties that might affect the responsiveness, like box-sizing.
Follow-ups
  • How would you handle different styles for portrait and landscape orientations?
  • What additional features would you add to make the div more interactive or visually appealing?
What the Question Tests
  • Understanding of CSS media queries for implementing responsive designs.
  • Ability to dynamically create and manipulate HTML and CSS using JavaScript.
  • Conceptual knowledge of responsive design principles.

This question effectively gauges a candidate’s skill in creating responsive web designs, a critical aspect of modern web development. It tests their technical knowledge of CSS and JavaScript and their understanding of designing web pages that adapt to different screen sizes and orientations.

6. Implementing a Function to Apply a CSS Animation

Task Develop a JavaScript function applyAnimation that applies a CSS keyframe animation to an HTML element. The animation should transition the element’s background color from red to blue over 5 seconds.
Input Format One argument: a string representing the id of an HTML element.
Constraints
  • The id must correspond to an existing HTML element.
Output Format The function does not return a value but modifies the specified element’s style to apply the animation.
Sample Input applyAnimation(‘myDiv’);

Suggested Answer

function applyAnimation(id) {

    let element = document.getElementById(id);

    let style = document.createElement(‘style’);

    style.innerHTML = `

        @keyframes colorChange {

            0% {background-color: red;}

            100% {background-color: blue;}

        }

        #${id} {

            animation: colorChange 5s;

        }

    `;

    document.head.appendChild(style);

}

Code Explanation

The applyAnimation function first finds the HTML element with the given id using getElementById. It then creates a style element, setting its innerHTML to define a @keyframes animation named colorChange. This animation changes the background color from red to blue. The CSS rule applies this animation to the element with the specified id, setting the animation duration to 5 seconds. The style element is finally appended to the document’s head.

Common Mistakes to Watch Out For
  • Not correctly defining the keyframes in the CSS.
  • Forgetting to append the style tag to the document, resulting in the animation not being applied.
  • Not handling potential conflicts with other existing styles or animations on the element.
Follow-ups
  • How would you modify the function to include easing functions for the animation?
  • Can this function be extended to support other types of animations or multiple elements?
What the Question Tests
  • Understanding of CSS keyframe animations and their implementation.
  • Ability to manipulate HTML elements and CSS using JavaScript.
  • Knowledge of creating dynamic and engaging visual effects using CSS.

This question is a great way to assess a developer’s skills in creating advanced visual effects with CSS animations, a key component in modern, interactive web design. It tests the integration of JavaScript and CSS for dynamic style manipulation, a common requirement in web development projects.

7. Creating a CSS Variable Manipulation Function

Task Create a JavaScript function changeTheme that changes the value of the CSS variable –theme-color for a specified HTML element to a given color.
Input Format Two arguments: a string representing the id of an HTML element and another string representing a valid CSS color.
Constraints
  • The id must correspond to an existing HTML element.
  • The color must be a valid CSS color.
Output Format The function modifies the CSS variable of the specified element but does not return a value.
Sample Input changeTheme(‘myDiv’, ‘purple’);

Suggested Answer

function changeTheme(id, color) {

    let element = document.getElementById(id);

    element.style.setProperty(‘–theme-color’, color);

}

Code Explanation

The changeTheme function locates the HTML element using getElementById. It then uses the setProperty method to change the value of the CSS variable –theme-color to the specified color for that element.

Common Mistakes to Watch Out For
  • Not ensuring that the specified element exists in the document.
  • Using an incorrect method to set the CSS variable value.
  • Not handling different formats of CSS color values properly.
Follow-ups
  • How would you extend this function to modify multiple CSS variables at once?
  • Can you adapt this function to apply the theme change to the entire webpage rather than just one element?
What the Question Tests
  • Knowledge of CSS Variables (custom properties) and their manipulation through JavaScript.
  • Ability to dynamically modify styles in response to user interactions or other conditions.
  • Understanding of more advanced CSS features and how they interact with JavaScript.

This question challenges a candidate’s ability to integrate JavaScript with advanced CSS features. CSS variables are increasingly important in modern web design for creating maintainable, scalable, and dynamic styles. This task tests both technical skills and conceptual understanding of these contemporary web development practices.

Conclusion

Selecting the right CSS interview questions is crucial for accurately assessing a candidate’s proficiency and fit for a web development role. These CSS interview questions, ranging from basic to advanced levels, offer a comprehensive insight into the candidate’s understanding of CSS, problem-solving skills, and ability to integrate CSS with JavaScript for dynamic web development.

Hiring managers and interviewers should approach these interviews with a clear strategy. The CSS interview questions should be tailored to reveal the depth of the candidate’s knowledge, coding style, and ability to adapt and apply their skills to solve complex problems.

We encourage hiring managers and technical recruiters to consider using Interview Zen, a platform that can streamline the interview process by providing tools and resources tailored for conducting comprehensive CSS interviews. Leveraging such a platform can enhance the efficiency and effectiveness of the recruitment process, ensuring that the right talent is identified for your web development needs.

Take the first step towards building a robust and skilled web development team with Interview Zen.

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