CSS

CSS is an acronym for 'Cascading Style Sheets' and is a style sheet language that specifies how a webpage looks. CSS is one of three technologies that are the primary makeup of all websites on the internet (with the other two being HTML and JavaScript). Other programming languages or frameworks (such as PHP) can be used to make up a website, but the end result (or output) of those other languages is always some combination of HTML, CSS, and JavaScript.

A CSS document contains style rules that define the particulars of how elements within an HTML document are displayed by a web browser. Style rules in a CSS document can control just about every aspect of how each element within a webpage appears, from positioning, sizing and spacing, layout, and order, to color, background, shadow effects, and more. CSS defines every aspect of how this page looks: the amount of space between this text and the edges of the 'card' it sits on top of, the rounding of the corners of the 'card', the shade of the black background behind everything within the page, the position of the navigational arrows to view the previous or next entries in this glossary; it is all specified by CSS style rules.

How does CSS affect SEO?

CSS doesn't directly affect search rankings or SEO in any way, but it can be used in conjunction with HTML to indirectly affect SEO, allowing you to achieve a desired look for a page without making any sacrifices when setting up a proper HTML structure. For example, since search engines look at the content of a page from top to bottom based on the HTML structure, it makes a big difference if things like sidebar content come before the main content. However, with CSS you can lay out your HTML in a way that emphasises what is most important and still maintain whatever look you want for users actually viewing the page.

Or as another example, every image on a page is taken into account in some way when a webpage is crawled and indexed by a search engine. This is typically a good thing, but what if you have an image that is only there for aesthetic purposes and doesn't actually add anything of consequence to the page? That image being crawled by the search engine could be drawing some attention away from what is really important on the page. Well, in this case, CSS can come to the rescue! While search engines crawl every image on the page, they do not (typically*) look at styling, so with a bit of clever HTML and CSS, you can replace an existing image with a 'background-image' instead.

*Theoretically, search engines have evolved to a point where they do look at styling enough to understand whether or not content is actually visible, and can actually penalise a page for having content that isn't visible to users as it can be interpreted as an attempt to manipulate the search engine's rankings.

Furthermore, search engine rankings can be dramatically affected by user engagement, so using CSS to create a website that is aesthetically pleasing and easy to navigate can absolutely have an effect on SEO as well.