26 Top CSS Interview Questions and Answers (2024)

Blog / 26 Top CSS Interview Questions and Answers (2024)

CSS is one of the cornerstones of web design and is a crucial skill for any web developers.

If HTML is the noun and JavaScript is the verb, then CSS is the adjective that completes the basis of the web development trifecta.

Whether you're a seasoned css veteran or a complete newbie these questions will help you nail any CSS related interview questions.

Q1.

What is CSS?

Junior

CSS (Cascading Style Sheets) is a markup language used for styling and formatting web pages, controlling elements' visual presentation, such as colors, fonts, spacing, and layout.

Q2.

Explain the CSS Box Model

Junior

The CSS Box Model is a concept that defines how an HTML element is structured, with content at its core, surrounded by padding, border, and margin layers that control its size, spacing, and appearance.
Example:
- width and height set the dimensions of the content area.
- padding creates space between the content and the border.
- border defines a border around the content with a 2-pixel solid line.
- margin sets space around the border to control the element's spacing from other elements.

Q3.

Explain cascading in CSS.

Junior

Cascading in CSS refers to the way styles are applied to HTML elements based on their specificity, source order, and inheritance, allowing multiple style sheets and styles to "cascade" into a final design.

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Q4.

What is the float property used for in CSS?

Junior

In CSS, the float property is used to place an element to the left or right of its container, allowing text and inline elements to wrap around it. Commonly used for layouts and image positioning.

Q5.

What is the difference between inline, inline-block, and block?

Junior

Inline: Elements don't start on a new line, and only occupy necessary width. No width/height setting; margin and padding affect only horizontally.
Block: Elements start on a new line and occupy the full width available. Width/height can be set; margin and padding affect all sides.
Inline-Block: Mix of inline and block. Elements flow like inline but can have width/height like block.

Q6.

How can you use media queries for mobile devices?

Junior

Media queries in CSS are used to apply styles based on device characteristics, such as screen size. For mobile devices, common practices include:

Setting Viewport: Include a viewport meta tag in the HTML head for proper scaling. <meta name="viewport" content="width=device-width, initial-scale=1">.
Defining Breakpoints: Create media queries for specific screen sizes. For example:

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Q7.

What is responsive web design?

Junior

Responsive Web Design is an approach to web design aimed at crafting sites to provide an optimal viewing and interaction experience across a wide range of devices. Key features include:
- Fluid Grids: Layouts that scale gracefully to fit any screen size.
- Flexible Images: Images that resize within their containing elements.
- Media Queries: CSS techniques that apply styles based on device characteristics.

Q8.

Explain the order in which styles are applied in CSS.

Mid

The order in which styles are applied in CSS is determined by a combination of three main factors: specificity, source order, and inheritance.
- Specificity: This is the primary factor. Specificity is a measure of how precisely a CSS selector matches a set of elements. Selectors with higher specificity override those with lower specificity.
- Source Order: When two selectors have the same specificity, the one that appears later in the CSS code takes precedence. This is known as the source order rule. It means that if you have two equally specific rules, the second one will override the first one.
- Inheritance: Some CSS properties are inherited by child elements from their parent elements, unless overridden. For example, font and color properties are often inherited. This means that if you set a property on a parent element, it can affect the child elements unless they have their own specific rules.
- Importance: The !important declaration in CSS can override the specificity and source order. When !important is used on a CSS property, it becomes the most important and overrides other properties, regardless of their specificity or source order.

Q9.

What is Flexbox?

Mid

Flexbox, or the Flexible Box Module, is a layout model in CSS that provides a more efficient way to lay out, align, and distribute space among items in a container, even when their size is unknown or dynamic.
Key features:
- Direction-Agnostic: Unlike traditional layouts (block is vertically-based, inline is horizontally-based), Flexbox works in any direction.
- Container Properties: Control the layout's direction, wrap, alignment, and spacing.
- Item Properties: Control the order, alignment, flexibility, and size of the items.
- Responsive Layout: Flexbox makes it easier to design a flexible responsive layout structure without using floats or positioning.

Q10.

What does Accessibility (a11y) mean?

Mid

Accessibility (abbreviated as "a11y" where "11" stands for the 11 letters omitted) refers to the design and creation of websites, tools, and technologies that are usable by all people, including those with disabilities.

Q11.

What is the difference between CSS variables and Pre-processor Variables (SASS, LESS, Stylus)?

Mid

Scope and Runtime: CSS Variables can be changed at runtime and have actual scope within the CSS DOM, while pre-processor variables are compiled into static CSS and can't be changed post-compilation.
Processing: CSS Variables are processed in the browser, allowing dynamic changes. Pre-processor variables are processed during the server-side build process.
Compatibility: CSS Variables are supported in modern browsers but not in older ones, whereas pre-processor variables work in all browsers as they compile into standard CSS.
Dynamic Capabilities: CSS Variables can be manipulated with JavaScript at runtime, unlike static pre-processor variables.

Q12.

What is Tailwind?

Mid

Tailwind CSS is a utility-first framework for creating custom designs rapidly. It offers low-level utility classes for design elements like spacing, sizing, and typography, enabling flexible and responsive design directly in HTML.

Q13.

Define z-index.

Mid

z-index in CSS is a property that sets the stack order of specific elements.
An element with a higher z-index is rendered in front of an element with a lower index. It's used for controlling the vertical stacking order of elements that overlap each other.

Q14.

What are the major differences between CSS3 and CSS2?

Mid

Modules: CSS3 is split into modules (like Selectors, Box Model, Backgrounds and Borders) for easier maintenance and updates. CSS2 was a single, monolithic specification.
New Features: CSS3 introduced new features like animations, transitions, gradients, flexbox, grid layout, and media queries for responsive design. CSS2 lacked these advanced features.
Browser Compatibility: CSS3 features are often implemented progressively across browsers, while CSS2 features generally have wider and more consistent support.
Syntax and Capabilities: CSS3 supports more complex selectors and properties, offering greater flexibility and control in styling compared to CSS2.

Q15.

What does !important mean in CSS?

Mid

In CSS, !important is used to override other style rules, making the specified rule take precedence regardless of specificity. Its use is discouraged as it complicates CSS maintenance and debugging.
For example, color: red !important; will ensure the element's text color is red, even if other style rules target the same element with different color values.

Q16.

Explain the different values of the CSS position property.

Mid

static: Default value; elements flow in the order they appear in HTML.
relative: Positioned relative to its normal position, allowing top, right, bottom, left adjustments.
absolute: Positioned relative to the nearest positioned ancestor, removed from the normal flow.
fixed: Positioned relative to the viewport, stays in place during scrolling.
sticky: Behaves like static until scrolled to a certain point, then acts like fixed.

Q17.

What are Vendor prefixes?

Mid

Vendor prefixes in CSS are a way for browser manufacturers to introduce support for new CSS features before they become standardized. These prefixes ensure that the experimental or non-standard features can be used in specific browsers, without affecting how the page is rendered in browsers that don't support these features yet. Common vendor prefixes include:
- -webkit- for Chrome, Safari, newer versions of Opera.
- -moz- for Firefox.
- -ms- for Internet Explorer and Microsoft Edge.
- -o- for older versions of Opera.
Example:

Q18.

What are pseudo-classes?

Mid

Pseudo-classes in CSS are keywords added to selectors that specify a special state of the selected elements. They allow you to define a particular style for an element when it's in a certain state.
Examples:
- :hover: Styles the element when it’s hovered over by a cursor.
- :focus: Applies style when the element is focused (like input fields).
- :active: Styles the element during the time it’s activated (like when a button is clicked).
- :visited and :link: Style links depending on whether they have been visited.
- :first-child and :last-child: Targets the first or last child element within its parent.
- :nth-child(): Styles an element based on its position in a group of siblings.

Q19.

What does the :root pseudo-class refer to?

Mid

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Q20.

What is the difference between {visibility: hidden} and {display: none}?

Mid

Q21.

Define gradients in CSS.

Mid

Q22.

What are pseudo-elements, and why are they useful?

Senior

Q23.

What is the CSS Grid System?

Senior

Q24.

When does DOM reflow occur?

Senior

Q25.

How does CSS work under the hood?

Senior

Q26.

What is PostCSS?

Senior