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CSS Performance Optimization Quiz

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Question 1/15

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

Select your answer

It guarantees fonts will load faster than any other setting.

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

It reduces overall CSS file size.

It disables custom font usage entirely.

Question 2/15

Which CSS technique might be used to ensure layout transition animations are smooth with minimal repaint and reflow?

Select your answer

Using CSS animations on properties like width and height.

Employing properties like

transform

and

opacity

, which can be handled by the GPU.

Utilizing JavaScript timers to precisely control animations.

Avoiding transitions by using instant changes.

Question 3/15

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

Select your answer

Recalculation of specificity during changes.

Style resolution during animations.

Selector matching in the computed view.

Parsing of raw CSS files.

Question 4/15

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.

Adding each element individually with a delay.

Loading CSS styles inline instead of with external resources.

Applying

display: none

before adding and then updating styles.

Question 5/15

Why is it recommended to avoid complex CSS selectors for performance optimization?

Select your answer

Complex selectors increase specificity issues.

Browsers do not fully support complex selectors consistently.

Complex selectors increase file size significantly.

Complex selectors make style recalculations slower because they can be costly to evaluate by traversing the DOM.

Question 6/15

Which of the following CSS rules will most likely lead to a performance bottleneck due to inefficient selector usage?

Select your answer

div > p

div + p :nth-child(3)

.container *[data-attr]

.banner > .title

Question 7/15

Which of these events would likely be most impacted by poor CSS performance?

Select your answer

Initial load time.

Click event responsiveness.

Page unload time.

Scroll performance.

Question 8/15

How does removing unused CSS media queries contribute to performance improvement in web applications?

Select your answer

It frees up thread processing used for CSSOM generation.

It solidifies CSS specificity rules.

It reduces file size, leading to faster download times and less parsing by the browser.

It decreases render time during dynamic viewport changes.

Question 9/15

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

Select your answer

They do not work with JavaScript CSSOM.

They can only be used for colors.

They are not yet supported in all browsers.

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

Question 10/15

How does using CSS pre-processing tools like SASS or LESS improve CSS performance?

Select your answer

They help organize and manage styles, reducing redundancy and file size before delivery.

They enable client-side preprocessing.

They inherently make styles render faster.

They utilize server-side caching automatically.

Question 11/15

Which of the following scenarios can result in a repaint of the document in browser rendering?

Select your answer

Animating the position using CSS

transform

Switching element visibility with

opacity

Changing the font family used by an element.

Changing the text color using

color

property.

Question 12/15

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

Select your answer

position: absolute

float

@font-face

flex

Question 13/15

Which of the following methods would effectively help async load CSS to avoid render-blocking?

Select your answer

Use a

<link rel='stylesheet'

element with

media='print'

and change the media type once loaded.

Inline all CSS into the HTML document.

Use a CDN for all CSS assets.

Load CSS with JavaScript dynamically.

Question 14/15

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

Select your answer

Increased parsing time due to redundancy.

Cross-browser rendering issues.

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

Validation errors in the HTML.

Question 15/15

Why should you avoid using

selectors in performance-critical CSS?

Select your answer

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

They increase CSS specificity unnecessarily.

They only work in older browsers.

Browsers have slower support for these selectors.

Your Results

You did not answer any questions correctly.

Your Answers

Question 1/15

😊 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 guarantees fonts will load faster than any other setting.

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

It reduces overall CSS file size.

It disables custom font usage entirely.

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 2/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which CSS technique might be used to ensure layout transition animations are smooth with minimal repaint and reflow?

Available answers

Using CSS animations on properties like width and height.

Employing properties like <pre><code>transform</code></pre> and <pre><code>opacity</code></pre>, which can be handled by the GPU.

Utilizing JavaScript timers to precisely control animations.

Avoiding transitions by using instant changes.

Using

transform

and

opacity

properties ensures that animations are offloaded to the GPU, minimizing the need for CPU-intensive style recalculations, repaints, and reflows.

Question 3/15

😊 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

Recalculation of specificity during changes.

Style resolution during animations.

Selector matching in the computed view.

Parsing of raw CSS files.

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 4/15

😊 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.

Adding each element individually with a delay.

Loading CSS styles inline instead of with external resources.

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

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 5/15

😊 Your answer was correct 🙁 Your answer was incorrect

Why is it recommended to avoid complex CSS selectors for performance optimization?

Available answers

Complex selectors increase specificity issues.

Browsers do not fully support complex selectors consistently.

Complex selectors increase file size significantly.

Complex selectors make style recalculations slower because they can be costly to evaluate by traversing the DOM.

Complex CSS selectors can lead to slow style recalculations as every element level in the DOM must be evaluated, potentially increasing the computational cost.

Question 6/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following CSS rules will most likely lead to a performance bottleneck due to inefficient selector usage?

Available answers

<pre><code>div + p :nth-child(3)</code></pre>

<pre><code>.container *[data-attr]</code></pre>

<pre><code>.banner > .title</code></pre>

The selector

div + p :nth-child(3)

uses a pseudo-class (:nth-child) and a sibling selector (+), which can be computationally expensive because the browser may need to examine a significant portion of the DOM to find matching elements.

Question 7/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of these events would likely be most impacted by poor CSS performance?

Available answers

Initial load time.

Click event responsiveness.

Page unload time.

Scroll performance.

Poorly optimized CSS can severely impact scroll performance as the browser might need to recalculate styles or layouts, leading to janky or sluggish scrolling behavior.

Question 8/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does removing unused CSS media queries contribute to performance improvement in web applications?

Available answers

It frees up thread processing used for CSSOM generation.

It solidifies CSS specificity rules.

It reduces file size, leading to faster download times and less parsing by the browser.

It decreases render time during dynamic viewport changes.

Unused CSS media queries increase the file size and complexity without contributing to functional styling, meaning removing them leads to a smaller CSS footprint and faster parsing.

Question 9/15

😊 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

They do not work with JavaScript CSSOM.

They can only be used for colors.

They are not yet supported in all browsers.

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

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 10/15

😊 Your answer was correct 🙁 Your answer was incorrect

How does using CSS pre-processing tools like SASS or LESS improve CSS performance?

Available answers

They help organize and manage styles, reducing redundancy and file size before delivery.

They enable client-side preprocessing.

They inherently make styles render faster.

They utilize server-side caching automatically.

CSS preprocessors like SASS and LESS allow for variable use, nesting, and includes that can reduce redundant CSS, leading to smaller file sizes before they reach the client.

Question 11/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following scenarios can result in a repaint of the document in browser rendering?

Available answers

Animating the position using CSS <pre><code>transform</code></pre>.

Switching element visibility with <pre><code>opacity</code></pre>.

Changing the font family used by an element.

Changing the text color using <pre><code>color</code></pre> property.

Changing the text color using the

color

property causes a repaint, as it updates how the pixels of an element are displayed visually, even though it doesn't alter its position or trigger a reflow.

Question 12/15

😊 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 13/15

😊 Your answer was correct 🙁 Your answer was incorrect

Which of the following methods would effectively help async load CSS to avoid render-blocking?

Available answers

Use a <pre><code><link rel='stylesheet'</code></pre> element with <pre><code>media='print'</code></pre> and change the media type once loaded.

Inline all CSS into the HTML document.

Use a CDN for all CSS assets.

Load CSS with JavaScript dynamically.

By using a

<link rel='stylesheet' media='print'

approach, the stylesheet loads without blocking rendering initially. Once loaded, the media type can be changed with JavaScript to apply styles.

Question 14/15

😊 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

Increased parsing time due to redundancy.

Cross-browser rendering issues.

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

Validation errors in the HTML.

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 15/15

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

They increase CSS specificity unnecessarily.

They only work in older browsers.

Browsers have slower support for these selectors.

Using the universal selector

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