The top 25 CSS interview questions for 2020

These CSS developer interview questions will help you ascertain the experience, technical expertise and problem solving abilities of each candidate.
Jul 8, 2020 • 6 minute read
Ruchi Bhargava @RuchiBhargava1
Technical Co-pilot
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This interview questiions will help you hire the best CSS developer in 2020

CSS developers create stunning interfaces that both attract and retain viewers. They can transform a boring website into a stunning conversion engine. For this reason, this profession is in high demand globally. 

A perfect CSS developer has technical acumen and a strong aesthetic sense, but how do you know if a candidate possesses these qualities? 

We've compiled a list of the top CSS interview questions that will help you hire the best CSS developer in 2020. 

The 25 best CSS interview questions

1.  What is the function of overflow:auto?

Ans: This command is used to add the scroll bar to content only when it's needed.

2. What is the function of overflow:scroll?

Ans: This command is used to add scroll bars on both sides of the webpage.

3. List the different types of CSS selectors.

Ans: The four primary CSS selectors are:

● ID Selector

● Class Selector

● Element Selector

● Group Selector

4. What is the CSS command to make all the text paragraphs red in color?

Ans: The following command will get the job done:

p{color:red;}.

5. What's the default value of the CSS position attribute?

Ans: The default value of the CSS Position Attribute is static.

6. What is the function of the float property in CSS?

Ans: The float property is used to move entire containers to the right or the left. The text elements are wrapped around the container in this case.

7. What are the different methods to assign a certain color to a css element?

Ans: In CSS, a developer can assign and use a wide range of colors with different elements. In general, there are three different notations that can be used to assign colors to a CSS element.

Hexadecimal Notation

In this notation, the color code always begins with a # sign, followed by a case-insensitive hexadecimal code. For example, code #FF0000 is the color red in the RGB color space.

Direct RGB Notation

RGB, or Red, Green, and Blue notation is used to represent colors using their red, green, and blue components. Often, an alpha channel component can be used to denote the opacity levels of the element. RGB colors are defined using the RGB() CSS function. This function accepts the above-stated four components as parameters.

HSL Notation

The HSL notation stands for the Hue, Saturation, and Luminosity model. HSL colors are defined using the HSL() function and work similarly to the RGB model.

8. What is the CSS Z-index?

Ans: The CSS Z-index is used to denote the stacking order of the CSS elements that might overlap with one another. The default value of the Z-index is zero, and it can take either a positive or a negative value. Here, it's well to remember that an element with a higher Z-index is always stacked above an element with a lower one.

9. Explain CSS sprites.

Ans: CSS Sprites are used to combine multiple smaller images into a single bigger element. It's mainly used to design icons, as in the case of Gmail. 

Sprites are created using specialized sprite generators that pack multiple images into a single one. They also generate the CSS code required for integration in your style sheet file.

10. Explain CSS pseudo elements.

Ans: Pseudo-elements are keywords that are used with selectors in order to style a specific part of the selected elements. Pseudo-elements can be used to add decorations or markup elements.

11. List the various media types used in CSS?

Ans: CSS uses four kinds of media types:

●      "all" used for all media devices

●      "print" used for printers

●      "speech" for read-aloud screen readers

●      "screen" for multimedia device screens

12. Explain the difference between {visibility:hidden} and {display: none}.

Ans: {display: none} is used to hide a particular element on the page itself. These elements can be interacted with using the DOM. Also, there's no space allocated for the elements between other tags.

In contrast, when {visibility:hidden} is used, the element is rendered on the page, just not visible. This means space is allocated for the elements, just that they are not seen on the page.

13. What is specificity in CSS?

Ans: Specificity is the technique by which browsers can decide which property values are most relevant to an element. Specificity is based on the matching rules that are applicable to the different levels of CSS Selectors.

Put simply, specificity is a weighted value applied to a particular CSS declaration. In case multiple-element declarations have equal specificity, the final CSS declaration is applied to the element. Keep in mind that specificity only applies when the same CSS element has more than one declaration.

14. What is a flexbox In CSS?

Ans: A CSS Flexbox is a layout-related module introduced in CSS3. It's used to control and improve the alignment of dynamic elements within the container. The Flexbox container can modify the width or height of the children elements to occupy the space available based on screen sizes.

CSS designers and developers prefer to use the Flexbox layout due to its coding simplicity. What's more, even complex layouts can be achieved with relative ease. Unlike the block or online layouts, Flexbox is based on directionality and hence is easily understandable. 

15. How do browsers match elements with CSS selectors?

Ans: As a general rule, browsers match selectors from right to left, filtering DOM elements and moving from the child elements up to the parent elements. Here, the selector chain plays a definitive role, the shorter the chain, the faster the matching process.

16. Explain the difference between using translate() and absolute positioning.

Ans: The translate() function is a CSS transform value. Changing it does not trigger browser repaint or reflow, instead it triggers the compositions. Changing absolute positioning, on the other hand, does trigger reflow.

Another difference between the two methods is how they are rendered. The translate() function uses the GPU for rendering, whereas absolute positioning uses the CPU. This makes the translation process more efficient, results in faster renderings and smoother animations.

17. Explain the concept of BFC.

Ans: In CSS, BFC stands for Block Formatting Context, which determines web page renderings for block box layouts. New BFCs can be established for elements such as floats, table-cells, inline blocks, and any elements with an overflow value other than visible.

BFCs are important since without an established BFC, floating children cannot exist within the container. 

18. How does a CSS preprocessor work, and when should it be used?

Ans: A preprocessor is a type of CSS software that generates code using the preprocessor's unique syntax. There are a large number of CSS preprocessors that one can choose from, and many have feature-sets that are different from that of pure CSS, such as inheritance and nesting selectors. 

Usage is project-specific, but in general, preprocessors should be used in tasks that require a large amount of CSS coding, split over multiple files. At the end of the day, it all boils down to personal preference.

19. Explain Vendor Prefixes in CSS.

Ans: Vendor Prefixes are vendor-specific experimental CSS code that's included by browser developers for testing purposes. The codes are used to denote that the specific code is still in the development stage, and improper use may result in code breakdown.

Some popular vendor prefixes are as given below:

● -moz- for Mozilla Firefox

● -o- for old versions of Opera

● -ms- for Internet Explorer and Microsoft Edge

● -webkit- for any WebKit based browser, such as Chrome and Safari.

20. When is a good time to use CSS file splitting?

Ans: A coherent file structure is an essential part of the CSS source code organization. A single file with all the code (also known as a monolithic file) is good enough for smaller projects involving single developers.

For larger projects being developed on a team level, it's best to split and distribute the code across source files. Such modularity introduces a fluid task delegation structure. This ultimately leads to better productivity and CSS operation.

21. Define Functions and Mixins?

Ans: Put simply, these are blocks of code that return a single data value of any type. The operation of functions and mixins are very similar, though the two differ as follows.

In functions, the returned value can be assigned to any CSS property or passed to another function. In a mixin, the output compiles directly to a CSS style.

22. Using which css property can the position of a background image be controlled?

Ans: The said task can be easily accomplished using the background-position property.

23. What is a CSS gradient?

Ans: In CSS3, gradients are used to display a better transition between multiple colors. Gradients in CSS can be of two types: linear and radial.

24. Explain Tweening.

Ans: Tweening is a CSS animation effect that's used to smoothly blend one image into another. With Tweening, CSS developers can create fluid animations.

25. What Are The Three Methods Of CSS Integration?

Ans: CSS can be integrated into an HTML document using the following three methods:

● Inline CSS

● Internal CSS 

● External CSS

Final words

The above 25 questions present strategic esoteric concepts to help businesses hire the most brilliant CSS developers and also help aspiring candidates prepare for their upcoming job interview.

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