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CSS Performance Optimization Quiz

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Question 1/15

Which CSS feature, if used incorrectly, can lead to unnecessary repaints and reflows, negatively impacting performance?

Select your answer

position: absolute

float

flex

@font-face

Question 2/15

Why should you avoid using

selectors in performance-critical CSS?

Select your answer

They only work in older browsers.

They increase CSS specificity unnecessarily.

Browsers have slower support for these selectors.

They target every DOM element, causing all elements to be reconsidered during style recalculations.

Question 3/15

What technique prevents layout recalculations when adding a large number of CSS-modified elements to the DOM?

Select your answer

Using document fragments to insert elements in bulk.

Loading CSS styles inline instead of with external resources.

Applying

display: none

before adding and then updating styles.

Adding each element individually with a delay.

Question 4/15

What optimization benefit does using font-display: swap; provide for web fonts in CSS?

Select your answer

It disables custom font usage entirely.

It ensures fonts are always visible even if there is a delay in loading.

It guarantees fonts will load faster than any other setting.

It reduces overall CSS file size.

Question 5/15

How does critical CSS enhance the user experience specifically for performance?

Select your answer

It inlines the styles needed for the initial viewport, decreasing time-to-first-render and initial page load times.

It ensures all CSS is cached for subsequent page loads, improving speed.

It organizes the CSS into logical pieces reducing parse time.

It forces browsers to render pages without any styling initially.

Question 6/15

What is a potential downside of using CSS custom properties ( var(--my-variable-name) ) on very high-dynamic elements for performance?

Select your answer

The dynamic nature requires recalculations that could lead to performance bottlenecks if used excessively.

They can only be used for colors.

They are not yet supported in all browsers.

They do not work with JavaScript CSSOM.

Question 7/15

How does deferring or async loading of CSS affect page performance metrics like FCP (First Contentful Paint)?

Select your answer

It negatively affects FCP as CSS will load later, delaying initial rendering.

It has no effect on FCP but improves TTI (Time to Interactive).

It actually slows down FCP by adding additional steps before rendering.

It improves FCP by allowing the browser to paint content earlier without waiting for critical CSS.

Question 8/15

How can you optimize CSS animations for better performance in modern browsers?

Select your answer

Avoid using animations on any element.

Always use JavaScript to manage animations.

Use hardware-accelerated properties such as

transform

and

opacity

Reduce the use of CSS keyframes in animations.

Question 9/15

What issues can arise if CSS is not effectively minified before deployment?

Select your answer

Slower page loads due to increased file size.

More efficient debugging using source maps.

Incorrect specificity calculations.

Increased parse errors in specific browsers.

Question 10/15

Why is it advisable to use only @supports rules for checking variable CSS features?

Select your answer

Ensures the CSS is compatible across all browsers by default.

Directly keeps the CSSOM size smaller.

It's required for all new CSS standards.

Keeps the code cleaner and reduces the risk of applying unsupported CSS, improving performance stability.

Question 11/15

Which part of the CSSOM (CSS Object Model) might lead to layout thrashing during interactive operations like animations?

Select your answer

Style resolution during animations.

Parsing of raw CSS files.

Selector matching in the computed view.

Recalculation of specificity during changes.

Question 12/15

Which performance issue may arise from incorrect cascading of CSS styles in a large application?

Select your answer

Validation errors in the HTML.

Increased parsing time due to redundancy.

Cross-browser rendering issues.

Increased specificity leading to potentially higher recalculation times when styles change dynamically.

Question 13/15

What is a key downside of placing too much CSS inline in HTML for performance purposes?

Select your answer

Higher download time due to more HTTP requests.

It improves first-page rendering at the cost of subsequent loads.

Increased specificity can cause issues when overriding styles.

Inline CSS prevents caching of styles across document requests.

Question 14/15

What is the main advantage of using CSS Grid over CSS Flexbox for performance optimization?

Select your answer

CSS Grid is more widely supported by older browsers.

CSS Grid inherently reduces CSS file size.

CSS Grid allows layout definitions that reduce layout re-calculations.

CSS Grid is always more performant than Flexbox.

Question 15/15

Which technique allows efficient use of media queries for optimizing CSS performance?

Select your answer

Applying all styles globally and then overriding with specific breakpoints.

Creating separate stylesheets for each device breakpoint.

Always applying mobile styles first, then layering complexity with media queries using mobile-first principles.

Using media queries only for color changes.

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which CSS feature, if used incorrectly, can lead to unnecessary repaints and reflows, negatively impacting performance?

Available answers

<pre><code>position: absolute</code></pre>

<pre><code>float</code></pre>

When

position: absolute

is used incorrectly or excessively, it can increase the complexity of calculating the element's position, potentially leading to costly reflows.

Question 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

Why should you avoid using <pre><code>*</code></pre> selectors in performance-critical CSS?

Available answers

They only work in older browsers.

They increase CSS specificity unnecessarily.

Browsers have slower support for these selectors.

They target every DOM element, causing all elements to be reconsidered during style recalculations.

Using the universal selector

forces the browser to consider all DOM elements, leading to slower style recalculations, hence decreasing performance.

Question 3/15

😊 Your answer was correct 🙁 Your answer was incorrect

What technique prevents layout recalculations when adding a large number of CSS-modified elements to the DOM?

Available answers

Using document fragments to insert elements in bulk.

Loading CSS styles inline instead of with external resources.

Applying <pre><code>display: none</code></pre> before adding and then updating styles.

Adding each element individually with a delay.

Document fragments allow for elements to be inserted into the DOM in bulk, reducing the number of reflows and layout recalculations needed, thus providing better performance.

Question 4/15

😊 Your answer was correct 🙁 Your answer was incorrect

What optimization benefit does using font-display: swap; provide for web fonts in CSS?

Available answers

It disables custom font usage entirely.

It ensures fonts are always visible even if there is a delay in loading.

It guarantees fonts will load faster than any other setting.

It reduces overall CSS file size.

The

font-display: swap;

property ensures text is displayed immediately using a fallback font until the custom font can be loaded, preventing invisible text (flash of invisible text -- FOIT).

Question 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does critical CSS enhance the user experience specifically for performance?

Available answers

It inlines the styles needed for the initial viewport, decreasing time-to-first-render and initial page load times.

It ensures all CSS is cached for subsequent page loads, improving speed.

It organizes the CSS into logical pieces reducing parse time.

It forces browsers to render pages without any styling initially.

Critical CSS involves inlining the necessary CSS for the content above the fold into the HTML to ensure it renders immediately, without waiting for external resources to load, improving user-perceived load times.

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is a potential downside of using CSS custom properties ( var(--my-variable-name) ) on very high-dynamic elements for performance?

Available answers

The dynamic nature requires recalculations that could lead to performance bottlenecks if used excessively.

They can only be used for colors.

They are not yet supported in all browsers.

They do not work with JavaScript CSSOM.

CSS custom properties are resolved at runtime, meaning changes to them can cause recalculation that, if not managed carefully, can impact performance when applied to many dynamic elements.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does deferring or async loading of CSS affect page performance metrics like FCP (First Contentful Paint)?

Available answers

It negatively affects FCP as CSS will load later, delaying initial rendering.

It has no effect on FCP but improves TTI (Time to Interactive).

It actually slows down FCP by adding additional steps before rendering.

It improves FCP by allowing the browser to paint content earlier without waiting for critical CSS.

By deferring the load of non-critical CSS, the browser can prioritize rendering the viewport content, thus improving metrics such as First Contentful Paint (FCP).

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

How can you optimize CSS animations for better performance in modern browsers?

Available answers

Avoid using animations on any element.

Always use JavaScript to manage animations.

Use hardware-accelerated properties such as <pre><code>transform</code></pre> and <pre><code>opacity</code></pre>.

Reduce the use of CSS keyframes in animations.

Using properties like

transform

and

opacity

leverages GPU acceleration, improving animation performance compared to other properties that may trigger reflows or repaints.

Question 9/15

😊 Your answer was correct 🙁 Your answer was incorrect

What issues can arise if CSS is not effectively minified before deployment?

Available answers

Slower page loads due to increased file size.

More efficient debugging using source maps.

Incorrect specificity calculations.

Increased parse errors in specific browsers.

Not minifying CSS leads to larger file sizes, which in turn means longer download times and slower initial page loads, thus impacting the overall performance and user experience.

Question 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

Why is it advisable to use only @supports rules for checking variable CSS features?

Available answers

Ensures the CSS is compatible across all browsers by default.

Directly keeps the CSSOM size smaller.

It's required for all new CSS standards.

Keeps the code cleaner and reduces the risk of applying unsupported CSS, improving performance stability.

@supports

rules allow conditional application of CSS depending on browser support for certain features, helping prevent unsupported rules from processing, making CSS more stable and performant.

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which part of the CSSOM (CSS Object Model) might lead to layout thrashing during interactive operations like animations?

Available answers

Style resolution during animations.

Parsing of raw CSS files.

Selector matching in the computed view.

Recalculation of specificity during changes.

The style resolution during animations can cause layout thrashing if style reads and writes are not batched correlatively, as frequent recalculations can lead to dropped frames and jank.

Question 12/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which performance issue may arise from incorrect cascading of CSS styles in a large application?

Available answers

Validation errors in the HTML.

Increased parsing time due to redundancy.

Cross-browser rendering issues.

Increased specificity leading to potentially higher recalculation times when styles change dynamically.

Incorrect cascading in CSS can lead to excessive specificity, meaning changes to styles might require significant recalculation and reapplication of styles impacting performance, especially in large applications.

Question 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is a key downside of placing too much CSS inline in HTML for performance purposes?

Available answers

Higher download time due to more HTTP requests.

It improves first-page rendering at the cost of subsequent loads.

Increased specificity can cause issues when overriding styles.

Inline CSS prevents caching of styles across document requests.

While inline CSS can improve the initial page load, it prevents styles from being cached across requests, leading to longer load times for subsequent page views.

Question 14/15

😊 Your answer was correct 🙁 Your answer was incorrect

What is the main advantage of using CSS Grid over CSS Flexbox for performance optimization?

Available answers

CSS Grid is more widely supported by older browsers.

CSS Grid inherently reduces CSS file size.

CSS Grid allows layout definitions that reduce layout re-calculations.

CSS Grid is always more performant than Flexbox.

CSS Grid allows defining both rows and columns in a layout, often reducing the number of complex nesting and code needed, which can lessen layout recalculations compared to Flexbox used in certain scenarios.

Question 15/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which technique allows efficient use of media queries for optimizing CSS performance?

Available answers

Applying all styles globally and then overriding with specific breakpoints.

Creating separate stylesheets for each device breakpoint.

Always applying mobile styles first, then layering complexity with media queries using mobile-first principles.

Using media queries only for color changes.

A mobile-first approach involves applying base styles that are progressively enhanced using media queries as screen size or device capabilities increase, ensuring only necessary styles are applied initially, reducing overhead.