Important Things To Know Before Hiring A CSS Developer

Important Things To Know Before Hiring A CSS Developer
Kelly Sikkema

Hello, community. Modern web programming, regardless of which technology you ultimately use, is always based on the interaction of HTML, CSS, and JavaScript. From this point of view, I am not telling you anything new, and yet we are taking the numerous expanded options of the new versions of these technologies as an opportunity to start with the basics.

Why should you hire a CSS developer?

The answer is easy. This stylesheet language is solely responsible for the presentation (design) of the content. A CSS developer knows how to deal with CSS in a compact way and thus how to create the foundation for solid and modern web applications that can greatly benefit your business.

Today, I am going to light up an important topic – important things to know before hiring a CSS developer.

First of all, you need to be sure that his or her knowledge is good enough to work for you. Below I have mentioned a list of required knowledge for CSS developers and, as an additional plus, some CSS interview questions that will help you to choose the right candidate.

Required advanced knowledge for CSS developers

  • Integration of CSS

CSS3 has a modular structure, is continuously being developed, and not all modules have yet been standardized by the W3C consortium. Nevertheless, you can assume that the majority of the features are already supported by the current browsers. In individual cases, however, you actually have to check whether a selected function works in the browser used. There are basically three options for integrating CSS in HTML:

  1. Inline style: You write down the CSS style information directly in the HTML element. This is the worst possibility in terms of structure. The principle is like this: <h1 style = “font-family: Courier;“> The web blog </h1>. Such a style specification within an HTML tag only applies to the relevant HTML element in which this instruction was noted. This instruction must be repeated for another heading at level one. There are almost no reasons to use the inline style if it is necessary to test the effect of certain CSS statements.
  1. Internal style sheet: This is where you collect all the style instructions for a website and summarize them in the header area. The advantage: All style instructions are in a central location in the relevant document. For the same elements, for example for all headings on level h1 of the document, only one style is now required. The disadvantage is that the style instructions only apply to the document in question. The internal style sheet is also not recommended for larger projects.
  1. External style sheet: The information on styles is stored in separate CSS files. The CSS file is then referenced from the HTML document, i.e. it is integrated via <link>. The link attribute is placed in the head area, for example: <link rel = “stylesheet“ type = “text / css“ href = “style.css“>.

In this case, the CSS file is called style.css and then contains all the relevant style information. Another advantage: You can use the styles across multiple HTML documents.

  • Web Development Trends

The CSS system is constantly updating, so the candidate that you want to hire should follow all web development trends.

The matrix of possible operating systems, browsers, and browser versions alone ensures endless possibilities that something will work differently than expected.

There are extremely many concepts that the developer has to master in order to be able to write CSS well at all.

Maintaining CSS over the lifecycle of an application and keeping it clean is a great challenge, as refactoring is only possible to a limited extent and is sometimes out of the question due to intermediate dependencies or the use of a CMS (where HTML is sometimes stored in the database).

CSS interview questions

Ask these questions during the interview and due to answers think whether you can hire an employee or continue your search.

  1. What is DOM (Document Object Model) and how it is related to CSS?

The Document Object Model (DOM) is a cross-platform and language-independent application programming interface that treats an HTML, XHTML, or XML document as a tree structure, where each node is an object that represents a piece of the document.

Using the document object model, programmers can create documents, navigate their structure, and add, modify, or delete elements and content. The DOM defines interfaces that can be used to manipulate XML or HTML documents.

When the browser displays a document, it must combine the content of the document with its style information. The browser converts HTML and CSS to DOM (Document Object Model). The DOM represents a document in computer memory. It combines the content of the document with its own style.

  1. What is the difference between classes and IDs in CSS?

Identifiers – must be unique in the document. Elements can only have one ID attribute. Classes – can be reused for multiple elements in a document.

  1. Describe floats and how do they work?

Float is a CSS property. It can be used to place an element relative to its neighbors. In this case, the element remains in the flow, on the contrary to absolutely positioned elements.

#sidebar {

float: right; // Aligns the element to the right and all other elements flow to the left


  1. Explain CSS sprites, and how would you implement them on a page or site?

CSS sprites combine multiple images into one large image. This is a widely used icon technique (Gmail uses it). Each image has a corresponding CSS class with specific background-image, background-position, and background-size properties. To use this image, add the appropriate class to your element.


Reduce the number of HTTP requests for multiple images (only one request is required per sprite sheet). But with HTTP2, loading multiple images is no longer a problem. Preloading resources that won’t load until you need them, such as images that only appear in pseudo-state on hover.

  1. What is cross-browser compatibility?

This is the correct layout of the site through which the pages of the site are displayed the same way in different browsers. Not all CSS rules are equally supported by all browsers. Special prefixes are used for those browsers that support the prefixed property.

  1. What is a CSS preprocessor?

A CSS preprocessor is a program that allows you to generate CSS from your own unique preprocessor syntax. There are many CSS preprocessors to choose from, however, most CSS preprocessors will add some features that don’t exist in pure CSS, such as mixin, nesting selector, inheritance selector, and so on. These features make the CSS structure more readable and easier to maintain.

Here are some of the most popular CSS preprocessors:

Sass (SCSS)




  1. What’s the difference between “reset” and “normalize” CSS?

Reset – designed to remove all default browser styles for elements. For example, margins, padding, font sizes of all elements are reset to be the same. You will have to revisit the style for common typographic elements.

Normalization – keeps useful styles by default, not spreads everything out. This also fixes bugs for common browser dependencies.

  1. What are CSS Selectors? Name some of them.

A CSS selector is part of a CSS rule set that selects the content you want to style.

Let’s look at some types of CSS selectors:

Universal selector: *

Element type selector: ul, td

ID selector: #id

Class selector: .box

Any Descendant: #id .box

Child: #id> .box

Brother and sister: ~

  1. What are pseudo-elements?

A CSS pseudo-element is a keyword added to a selector that allows you to style a specific portion of the selected elements. They can be used to style (: first-line,: first-letter) or add elements to markup (combined with content: …) without having to change the markup itself (: before,: after).

  1. What is a CSS grid system?

A grid system is a framework that allows content to be combined vertically and horizontally in a consistent and easily manageable way. Grid systems have two key components: rows and columns.

What can you offer when you hire a CSS developer?

Yes, first of all, you are employing a developer and you have the full right to have a set of certain requirements for him. But you must also offer something instead.

Start from offering a friendly working atmosphere. Solutions should be found together, experiences, ideas, successes have to be shared. Be family-friendly, support further training, and don’t leave anyone out in the rain.

In order to make the working process for the developer interesting and fascinating, offer him the following:

  • Diverse projects
  • Free choice of the operating system – Windows, Mac, or Linux
  • Nice colleagues
  • Travel activities
  • Paid training and online courses
  • Family-friendly organization of working hours
  • No weekend work

So, take into account all the written above and you will hire the best CSS developer that will bring your company to a new level. Good luck!

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