CSS is the abbreviation for Cascading Style Sheets which basically describes how HTML will be displayed to the user or in more simpler words, adding fonts and colour to a webpage. It generally saves the developer a lot of time and effort as it controls the layout of a number of webpages at once by defining styles in web pages which includes the design and layout. Dependent on devices (iOS/Android) and screen sizes there are many variations therefore CSS helps to define this as well.
CSS was actually created by the World Wide Web Consortium to solve a huge problem that they had with HTML. Because HTML was never meant to contain tags for the formatting of a web page it caused a huge issue for developers when they tried to add them to the latest version of HTML. This made the process of adding different fonts and colour to large web pages a lot longer than it needed to be therefore wasting time and money! As a result CSS was made with the intention of removing the style formatting from HTML. What’s HTML you ask? Check out my recent blog 'What is...HMTL?'.
A lot of time is saved using CSS as files are usually saved externally in a .css file where a developer can change how a whole webpage looks by changing just one thing in the file. If you think of the file like a house that you want to change the carpet to wooden flooring, instead of removing the carpet, underlay and floorboards you would simply just take up the carpet, level the surface and put the wooden flooring down keeping the original floorboards. This is effectively what CSS has done for web development by streamlining the process which was otherwise quite difficult when trying to use HTML for everything.
Roles that will generally use CSS are software developers which are generally more Front-End. A competent Front-End Developer will be proficient in JavaScript, HTML and CSS with the three going hand-in-hand with one another. In recent years, Front-End Developers have started using modern JavaScript frameworks such a React and Vue which help to further streamline processes of web development.