The CSS stylesheet contains all styles for your blog—it’s the one styling document to rule them all!
A stylesheet is the document that contains the CSS code that designs (styles) your blog or website. The stylesheet is typically titled style.css.
Here's what a stylesheet looks like:
When you make a change in your stylesheet, it will affect the whole site—so be careful to not change a style in the document to just make a small change you want in just one place.
For example, let’s say you decide to change your font size for Heading 2 to be 32px. Well, it might make one page look great, but suddenly your blogpost headlines are too big and your nav bar looks crowded. It’s better to write new code to make very specific changes than to edit existing code for a small change.
However, if you want to make a big change, like change the color of all of the buttons on your website, then you’d go ahead and make an edit to the existing code.