CSS, or Cascading Style Sheets, is a type of programming language and style sheet language. Essentially, where the purpose of HTML is to mark up the text being put on a website (such as through font and color changes), the purpose of CSS is to give that text structure, whether it be via a website on your desktop computer, your mobile phone, or elsewhere. This entails providing not only the structure for the HTML to be placed, but also to design your website however you deem fit (though we do strongly recommend that how you see fit to design it is actually a good idea).
Much like HTML, CSS is a necessary component of any functioning website. If the website did not have a CSS, at that point it simply does not exist. Even if you only stick with the default CSS for a website, that is still a CSS. Without HTML, you won't have the text itself. Without CSS, you won't have the structure to display HTML's accomplishments.
Does every website use CSS?
CSS is required for any and all websites to function normally, as it is a basic building block of any website (and indeed, every website). If you are designing your own website, it would be vitally important that you come to better understand how CSS works, and how it can be made to work for you.
What is JavaScript
JavaScript is a type of scripting or programming language that many websites use for the more complex aspects of said websites. Examples of these complex features include animating graphics on the website, updating content, videos, etc. JavaScript is significantly more difficult to wrap your head around than either HTML or CSS, and as such, when you go into learning it, make sure that you are taking it all seriously and pay close attention to even the minor details of the process. Having a good understanding of CSS will not be enough to help you better understand JavaScript, and this becomes especially true for if your only experience is working with HTML.
Does every website use JavaScript?
While JavaScript is not quite as ubiquitous as HTML in terms of presence on websites across the Internet, it is pretty darn close. At the beginning of 2022, it was reported that 97.9 percent of websites utilize JavaScript in some form or another. However, it should be noted that this percentage does not take into account what percentage of JavaScript use is for the basic functioning of a website, rather than for something entirely incidental to the improvement of the website. It also means that disabling JavaScript locks you out of quite a few websites, at least in terms of accessing them at their most feature-full and stable.