CSS Interview Questions and Answers for 10 years experience

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100 CSS Interview Questions and Answers

  1. What is the difference between inline, block, and inline-block display properties?

    • Answer: Inline elements only take up as much width as necessary and don't start on a new line. Block elements take up the full width available and always start on a new line. Inline-block elements combine features of both; they take up only the width they need but can be styled with width and height properties and can sit side-by-side on the same line.

  2. Explain the concept of the box model.

    • Answer: The box model describes how an element's dimensions are calculated, including content, padding, border, and margin. Understanding this is crucial for accurate layout and sizing. Content is the actual text or image; padding is the space inside the border; border is the border itself; and margin is the space outside the border.

  3. What are CSS selectors? Give examples of different types.

    • Answer: CSS selectors target HTML elements to which styles are applied. Examples include: element selectors (e.g., `p`), class selectors (e.g., `.myClass`), ID selectors (e.g., `#myId`), universal selector (`*`), descendant selectors (e.g., `div p`), child selectors (e.g., `div > p`), attribute selectors (e.g., `[type="text"]`), and more complex combinators like sibling selectors (+), general sibling selectors (~).

  4. How do you center an element both horizontally and vertically?

    • Answer: There are several ways, depending on the context. For single-line text within a container, `text-align: center;` and `line-height: container-height;` can be used. For block-level elements, Flexbox or Grid offer the most straightforward solutions. For example, using Flexbox: `display: flex; justify-content: center; align-items: center;`.

  5. Explain the difference between `position: relative`, `position: absolute`, and `position: fixed`.

    • Answer: `position: relative` positions an element relative to its normal position. `position: absolute` positions an element relative to its nearest positioned ancestor (or the initial containing block if none are found). `position: fixed` positions an element relative to the viewport (browser window).

  6. What is the `z-index` property and how does it work?

    • Answer: `z-index` specifies the stack order of elements which overlap. A higher `z-index` value will be placed on top of elements with lower values. It only works on positioned elements (relative, absolute, fixed).

  7. What are CSS preprocessors like Sass or Less, and what are their benefits?

    • Answer: CSS preprocessors extend CSS with features like variables, nesting, mixins, functions, and more. This improves code organization, maintainability, and reusability, making larger CSS projects much more manageable. They compile into regular CSS for browser use.

  8. Explain the concept of CSS specificity and how it resolves style conflicts.

    • Answer: CSS specificity determines which styles are applied when multiple rules apply to the same element. Specificity is calculated based on the types of selectors used (inline styles have highest specificity, then IDs, classes, and finally element selectors). The most specific rule wins.

  9. What is the cascade in CSS and how does it work?

    • Answer: The cascade in CSS determines which styles are applied when multiple rules conflict. It considers the order of stylesheets, the specificity of selectors, and the importance of rules. Later styles override earlier ones, unless specificity dictates otherwise.

  10. How do you use CSS to create responsive layouts?

    • Answer: Responsive layouts use media queries to apply different styles based on screen size, orientation, and other device characteristics. Techniques like fluid grids, flexible images, and viewport meta tags are also crucial.

  11. Explain the use of `@media` queries. Give examples.

    • Answer: `@media` queries allow you to apply different styles based on different screen sizes and other device characteristics. For example: `@media (max-width: 768px) { .container { width: 90%; } }` This applies a width of 90% to the `.container` class when the screen width is 768 pixels or less.

  12. What are CSS frameworks like Bootstrap or Tailwind CSS, and when would you use them?

    • Answer: CSS frameworks provide pre-built CSS components and styles to speed up development. Bootstrap offers a comprehensive set of ready-made components, while Tailwind provides highly customizable utility classes. They are useful for rapid prototyping and building consistent UIs, saving time on writing custom CSS.

  13. Explain the concept of CSS variables (custom properties).

    • Answer: CSS variables, declared with `--variable-name: value;`, allow you to store values and reuse them throughout your stylesheet. This improves maintainability and allows for easy theming and customization.

  14. How do you optimize CSS for performance?

    • Answer: Optimization techniques include minimizing CSS file size (using tools like CSS minifiers), using efficient selectors, avoiding unnecessary specificity, using CSS sprites for icons, and leveraging browser caching.

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