CSS variables not being evaluated/highlighting

I use Pigments in SVG files, and while the colors are highlighted in CSS variable declarations, they are _not_ highlighted when the variable is used:

I checked to see if it was just a problem with inline properties, or just SVG, but it also occurs in HTML:

When I run `Pigments: Reload` on an open project I get the following:
```
Found:

90 path(s)
0 variables(s) including 0 color(s)
```
(there are a whole lot of color variables in this project)

From having a look through the issues, it seems that this is working for most other people - is there a setting that I should check on? I think I still have mostly the defaults though.

----

Pigments version: **0.40.6**
Atom version: **1.53.0**
OS: **elementary OS 5.17** (Built on Ubuntu 18.04.4 LTS)

The issue is about CSS variable highlighting in SVG and HTML files not working. Start by examining the Pigments package's color parsing logic, likely in the main CoffeeScript files. Look for how variables are detected and highlighted in different file types. Check the project's variable extraction and matching code. Run the package in Atom's dev mode to see debug output and test changes.

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