Here are the Top 40 Advanced CSS Interview Questions and Answers that can help you prepare for front-end development interviews in 2025, covering deep CSS concepts, performance, architecture, and real-world application:

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Top 40 Advanced CSS Interview Questions and Answers

🔹 1. What is the difference between em, rem, %, and px in CSS?

• px: Absolute unit (e.g., 16px is always 16 pixels).
• em: Relative to the parent element’s font size.
• rem: Relative to the root element’s font size.
• %: Relative to the parent container.

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🔹 2. How do you create a responsive layout in CSS without media queries?

• Use flexbox, grid, clamp(), min(), max(), or fluid typography techniques like: font-size: clamp(1rem, 2vw, 3rem);

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🔹 3. Explain specificity in CSS.

• It determines which rule is applied when multiple rules match the same element.
• Order of precedence:
  • Inline styles > IDs > Classes > Elements
  • Calculated as a 4-value tuple (a,b,c,d):
    • #id = (0,1,0,0)
    • .class = (0,0,1,0)
    • element = (0,0,0,1)

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🔹 4. What is the difference between visibility: hidden and display: none?

• visibility: hidden hides the element but still takes up space.
• display: none removes the element from the document flow.

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🔹 5. What is a pseudo-element in CSS?

• Used to style specific parts of an element: p::first-line, div::before, div::after

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🔹 6. What is the stacking context in CSS?

• A 3D conceptual hierarchy where elements are layered.
• Created with position, z-index, opacity < 1, transform, etc.

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Top 40 Advanced CSS Interview Questions and Answers

🔹 7. How does the z-index work?

• Controls vertical stacking order.
• Only works on positioned elements (relative, absolute, fixed, or sticky).

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🔹 8. What are initial, inherit, and unset in CSS?

• initial: Resets to browser’s default value.
• inherit: Inherits from parent.
• unset: Resets to inherited if naturally inheritable, otherwise initial.

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🔹 9. How do CSS Grid and Flexbox differ?

• Flexbox: One-dimensional (row or column).
• Grid: Two-dimensional (rows and columns).

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🔹 10. What are media queries and how do they work?

• CSS rules based on viewport/device characteristics. @media (max-width: 768px) { body { font-size: 14px; } }

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🔹 11. What is the difference between relative, absolute, fixed, and sticky positioning?

• relative: Offset from original position.
• absolute: Positioned to nearest non-static ancestor.
• fixed: Positioned relative to viewport.
• sticky: Switches between relative and fixed based on scroll.

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🔹 12. What is the contain property in CSS?

• Used for CSS containment to optimize rendering: .card { contain: layout style; }

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Top 40 Advanced CSS Interview Questions and Answers

🔹 13. What are custom properties (CSS variables)?

• Reusable values defined with --: :root { --main-color: #333; }

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🔹 14. How to prevent layout shifts in CSS?

• Always define height/width.
• Use aspect-ratio.
• Avoid images without dimensions.

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🔹 15. How do you center an element vertically and horizontally?

Flexbox way:

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

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🔹 16. What is the difference between min-width, max-width, and width?

• width: Fixed size.
• min-width: Minimum allowed width.
• max-width: Maximum allowed width.

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🔹 17. What is calc() in CSS?

• Performs calculations: width: calc(100% - 60px);

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🔹 18. What is clamp() in CSS?

• Sets a value between min, preferred, and max: font-size: clamp(1rem, 2vw, 2rem);

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Top 40 Advanced CSS Interview Questions and Answers

🔹 19. How do transitions and animations differ in CSS?

• Transitions: Animate between states.
• Animations: Can be looped and controlled using @keyframes.

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🔹 20. How to optimize CSS for performance?

• Minify files
• Use shorthand
• Avoid deep nesting
• Eliminate unused styles
• Use critical CSS for above-the-fold

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🔹 21. What is a BEM (Block Element Modifier)?

• CSS naming convention: .btn--primary, .card__title

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🔹 22. How do you make a sticky header?

header {
  position: sticky;
  top: 0;
  z-index: 1000;
}

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🔹 23. What is the will-change property?

• Hint for browser optimizations: .element { will-change: transform; }

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🔹 24. How does the box-sizing property affect layout?

• content-box: Default, padding and border add to width.
• border-box: Includes padding and border in declared width.

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🔹 25. What is the difference between nth-child and nth-of-type?

• nth-child(n): Matches the nth child regardless of tag.
• nth-of-type(n): Matches the nth element of a type.

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Top 40 Advanced CSS Interview Questions and Answers

🔹 26. What is reflow and repaint in CSS rendering?

• Reflow: Affects layout → expensive.
• Repaint: Affects appearance (e.g., color).

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🔹 27. What’s the use of object-fit?

• Controls image scaling in containers: img { object-fit: cover; }

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🔹 28. How to apply styles to only the first row/column in a table?

table tr:first-child { background: #eee; }
table td:first-child { font-weight: bold; }

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🔹 29. How can you hide elements but make them accessible to screen readers?

.hidden-accessible {
  position: absolute;
  left: -9999px;
}

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🔹 30. How to use attribute selectors in CSS?

input[type="text"] { background: #eee; }

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🔹 31. What is a media feature in CSS?

• A condition inside a media query (e.g., min-width, orientation, prefers-color-scheme).

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🔹 32. How to create a triangle with CSS?

.triangle {
  width: 0; height: 0;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  border-bottom: 10px solid red;
}

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🔹 33. What is the difference between inline, block, and inline-block?

• inline: No height/width, respects flow.
• block: Takes full width.
• inline-block: Like inline but allows size.

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🔹 34. What is :has() in CSS?

• Parent selector (modern browsers): div:has(> input:checked) { border: 1px solid green; }

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🔹 35. How does mix-blend-mode work?

• Blends an element with its background: .blend { mix-blend-mode: multiply; }

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🔹 36. Explain isolation: isolate in CSS.

• Creates a new stacking context to avoid blend-mode effects.

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🔹 37. What is the use of aspect-ratio in CSS?

.card {
  aspect-ratio: 16 / 9;
}

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🔹 38. What is CSS Houdini?

• Low-level APIs that allow developers to extend CSS via JavaScript (e.g., Paint API, Typed OM).

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🔹 39. How to avoid flash of unstyled content (FOUC)?

• Use proper preload links
• Avoid delayed style loading
• Use server-side rendering for critical CSS

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🔹 40. What’s the difference between logical and physical properties in CSS?

• Physical: margin-left, padding-top
• Logical: margin-inline-start, padding-block-end — better for internationalization (RTL support).

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Top 40 Advanced CSS Interview Questions and Answers

Top 40 Advanced CSS Interview Questions and Answers

Top 40 Advanced CSS Interview Questions and Answers