CSS variables table, hex value doesn't correspond to token value

[wise-king-sullyman]

Now that the CSS variables aren't fixed values we'll probably either want to stop showing the hex values to encourage token use, or we will need to come up with an approach which can either show all theme values, or show the current theme value and update that value when the theme is changed.

As a temporary measure in #4110 I added a disclaimer to color values in the CSS vars table that states the hex value is for light theme only.