Using CSS variables in Dash

Does Dash support CSS variables, as in:

:root {
–custom-color: #F9F9F9;

.header {
background-color: var(–custom-color);

(here is the website describing how to do this:

I’d like to give my custom colors names, and CSS variables are one way to do that; they aren’t working in my code, so I wanted to make sure they were supported before I began troubleshooting.