The CSS working group is still trying to determine how the variables should best be represented in CSS. The designers favor declaring by using a reserved keyword, “var,” in front of a new ...

Support was first added for CSS variables in Firefox 29, and developers had been using variables in their CSS code for many years via compile-to-CSS languages such as Sass, LESS, or Stylus. These days ...

Chrome also supports using these new custom variables in JavaScript without any issues. CSS variables are very new though have been in the works for years — but they’re not widely supported yet.