Comments

Including comments in CSS is simple. You open with /* and end with */, like this:

/* This is a comment! */

Comments can be multiple lines long:

/* This is a comment!
  This is a continuation of the comment.
 And so is this. */

They can also occur anywhere within a style sheet except in the middle of a token (property name or value):

h1/* heading-level-1 */ {color /* foreground color */: 
   rgba(23,58,89,0.42) /* RGB + opacity */;}

HTML (properly SGML) comments (<!-- such as this -->) are permitted in style sheets so as to hide the styles from browsers so old that they don’t understand HTML 3.2. They do not act as CSS comments; that is, anything contained in an HTML comment will be seen and interpreted by the CSS parser.