CSS (an acronym for “Cascading Style Sheets”) is a formal language for describing the appearance of a document written using a markup language such as HTML or XML. It is mainly used to describe how a web page should look and for this purpose it can load additional web resources (such as images, fonts, or styles). As you probably guessed, such resources can be embedded in the CSS by encoding them to Base64, and sometimes it may improve the performance of the web-page.
As well as HTML, CSS supports Data URI to embed Base64 values. Of course, this does not mean that you need to embed all web resources in a CSS file. Therefore, do it wisely, and if you’re not sure, just don’t use it.
Below are listed some CSS properties that support Data URIs: