By using Lifewire, you accept ourGet to Know Cascading Style Sheets With This CSS Cheat Sheet CSS uses the same "block comment" syntax as the C-like languages - you start a comment with /*, and end it with */.. Add the opening comment tag before the code you'd like to comment out (disable); place the closing tag where you want the disabled portion to end. In this case, this comment lets someone reading the CSS file know that that particular line of CSS was intended to allow for using ems to set font size later in the CSS in a more intuitive base 10 way. A CSS comment is used to add explanatory notes to the code or to prevent the browser from interpreting specific parts of the style sheet. This trick can be handy when you're debugging, or when adjusting webpage formatting.