20+ Best CSS Interview Questions To Get Hired With

Knowing CSS is a critical part of landing any front-end engineering position. Below is my CSS interview question and answer guide. The difficult part about CSS is that while yes, there is a way to ensure you can show an interviewer that you have great experience with CSS. There may still some questions which are a bit more specific to the person asking you the question. CSS does have personal styles to it. Meaning, the way its used is quite flexible at times and because of that, some developers use the various methods of CSS differently. You can’t really prepare for that in your interview though, its just important to recognize that being the case that you can explain to an interviewer that there’s a few different ways that something might be achieved and that you are willing to explain the ways of which the question might be achieved.

css interview questions

Before we jump right in into the CSS interview questions and answers, I like to include a short video of a professional speaking about CSS. I find that its really helpful to see how other people are speaking about the subject. How they articulate the passion they have for this technical subject matter. It should be helpful for you going into the interview because its something that you can essentially emulate.

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CSS Interview Questions & Answers

1. What is the primary job of CSS?

The primary job of CSS is to provide the HTML elements with their appropriate styles, imagery and overall User Experience. The function of CSS is to make all websites look as the designer intended. Meaning, a custom experience so that all visitors understand they are on a differently branded website. Nearly all websites you visit have CSS controlling their display.

2. How do you include CSS on a website?

You include CSS on a website by using the script tag. The script tag has an href associated to it which is where you link to the CSS file. The type of asset is called a text/css file.

3. What is inline CSS?

Inline CSS is when you are defining a style on an HTML element directly. Meaning, if I have an HTML object, I am putting a style=“” tag within its object brackets and defining my CSS styles within that style tag directly.

4. Should incline CSS be used?

This was of great debate early on in the web but now has become industry standard, you should not use inline CSS. The reason for this is that it becomes difficult to manage. If you want to change styles of your website, you’ll have to hunt down and replace all of the inline CSS that is part of your HTML files. This would be extremely time consuming and not efficient. Instead, you can link to your CSS file once and then when you want to make changes, you can change it within one file and that change will be effected globally.

5. What is a CSS class?

A CSS class is essentially a CSS object which is being called or utilized in many places. This is best used for something like a font color or a font weight. Something where the class might be more universal than a single application.

6. What is a CSS ID?

A CSS ID is when something is strictly defined to a particular object. This is when you want to ensure no other styles can be inherited from any other CSS object.

7. What is the difference between a class and an ID?

The main difference between a class and an ID is how they are used. A class is used amongst many HTML objects, potentially even many HTML ID’s. It is best used for scenarios that are global, meaning if you want to change a font color to black, then you may have a class called “font-black” or something like that. In the instance of an ID, you are not going to be using those styles globally. They should only be called once and that should be the only time that style in particular is used.

8. What is SCSS?

SCSS or LESS is essentially compiled CSS. Compiled means that the CSS file has been compressed or merged from a series of files which potentially share similar coding patterns.

9. How do you appropriately use classes in CSS?

The way to appropriately use classes in CSS is to make them global and very specific. For a font-weight you would use “font-bold” or something similar for the class name and the class function. You would want to apply that class to the HTML objects which they are applicable for.

10. What font weights are used in CSS?

You can define font weights in two different ways. You can define them by a numeric value. From 100 to 700. 700 being the most bold and 100 being the most light. You can also define it by using bold, medium, light as actual words. For both of these methods, there is not one that is preferred. It usually depends on which font family you are using and what types of weights are available for that family.

11. What is letter-spacing used for?

Letter spacing effects the width between letters of words on the page. This is sometimes used to increase the readability of fonts which have some tighter kerning.

12. What is the ideal font size for readability?

Due to mobile devices being the primary source for which content and websites are now consumed by consumers, their readability habits have changed. The ideal font weight is about 18px to 24px in size. Which is actually quite large compared to the first origins of the web, where smaller font sizes like 11px were more commonly used.

13. How do you work with other engineers on CSS code?

Its really important that CSS files are built in a fashion that allows for easy collaboration. There needs to be some planning around what’s being built, where what’s being built may evolve towards and how the CSS files are going to progress over time. Its critical that all engineers who are collaborating on the CSS files are having these types of conversations. Its also critical that there’s some type of convention discussion happening between the engineers. There needs to be a common language that’s had between the engineers so that all code can be readable for all parties. Lastly, all CSS code should be checked into a version control system, something like GIT. Which can then allow for multiple engineers to contribute their efforts together as a whole and then eventually merge all changes into a single CSS file that’s used in a production environment, which means to be live and launched on the website it was intended for.

14. How do you change the colors of a font in CSS?

You change the colors of a font in CSS by using the “color” selector. You’d do this by saying “color: #FFF” which would then turn the color of something white. This is not be confused with background color. Color as a selector only changes what the color of elements are within the HTML block that it is being referenced.

15. What is a HEX code in CSS? And what’s the difference between HEX and RGB?

A HEX code is a 6 digit type of code that is used to reference colors on the color wheel. A HEX code may look like the following “#FFFFFF” when a RGB code may actually reference the 1-300 numeric values of particular colors. The main difference is that the RGB colors are more specific, when HEX colors are a bit more limited in their display. The use of this has evolved over the years as monitors have become far more advanced than early days of HTML/CSS when personal computers didn’t have the highest of quality displays to them. Today, displays and monitors can show many more colors than they could originally.

16. How do you effect opacity in CSS?

You can effect opacity in many ways. Opacity can effect opacity by using the “opacity” selector in CSS and then defining a value after it. For example “opacity:1” would then turn the opacity up to 100%, meaning that it has no transparency. If you are attempting to add opacity to a font, you would have to use RGBA for that, where the A stands for “Alpha” meaning transparency. It would still be a numeric value to 1, where 1 means 100%, thus no transparency.

17. What does CSS stand for?

The abbreviation CSS stands for Cascading Style Sheets.

18. What are some ways CSS files can go bad?

There are many ways CSS files can go bad, meaning that they are impossible to manage and sometimes need to start over. Usually, its when there’s some type of decay to the styling. If the company changes or the design of the website changes dramatically, the CSS files can start to contain code which isn’t being used by any HTML objects, and then the code can become bloated and difficult to deal with. Even more so, it can cause computational power to be used as well, especially when the CSS is being compiled. The CSS file containing styles, objects, classes and ID’s which aren’t being used any longer is definitely the number one way a CSS file can go horribly wrong.

19. What’s the ideal code length for CSS? Meaning, its overall number of lines inside the CSS code?

Depending on the size of company and website you are working with, the ideal length for CSS should be somewhere between 1000-3000 lines of code. It is often recommended to think about your functions as partials. Meaning, if the file is above 3000 lines of code that you should potentially split it off into another CSS file and define the intended use of the CSS within that file itself.

20. Why do some professionals use multiple CSS files?

For exactly the reason above. Professionals use multiple CSS files to be able to control the amount of code they are working with and control specific parts to their application and website with ease. The major use of this is to prevent any errors from happening by overriding code which is stable and also being able to manage the future development of code more strictly. Think about it like having many sticks in a fire vs. one log. It’s simply an easier way to manage something complicated.

21. Why would you use the “important!” function in CSS?

The use of “important!” is widely discussed. It is not normally a function you will want to use frequently. It is when there are conflicting styles being referenced within many classes. It essentially overrides any conflicting calls being made within the CSS file itself. Because of this, it is better to fix the conflict and think about how your HTML and CSS are structured together to make a better functioning piece of code.

Conclusion

Its better in these interview sessions to prepare yourself with the methodologies of the particular subject matter you are going over, so in this case CSS. If an interviewer is asking you to write CSS in a whiteboard or potentially pair program together, you should be able to do that just fine. CSS isn’t a particularly difficult language to learn. Mostly because it uses a lot of human language elements which is different than say, “C” as a programming language. Because of this, you’ll want to be verbally prepared to speak to process and how you treat your codebase more so than trying to be prepared with a number of ways you’d answer specific technical questions. Far in advance, a great trick would actually be to pull up the CSS files of the company you are interviewing with and try to study their particular style of writing their CSS and front-end code. Because all of this can be accessed publicly, this can be a great way to be ahead of your competition and stand out. Maybe even come prepared with some type of suggesting for improving their already working CSS files.

author: patrick algrim
About the author

Patrick Algrim is an experienced executive who has spent a number of years in Silicon Valley hiring and coaching some of the world’s most valuable technology teams.

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