Button text color is not using --button-filled-brand-text variable

[mangkoran]

We found the default Discord button use --button-filled-brand-text variable as text color. However, catppuccin currently use class selector (CMIIW) instead.

This breaks some custom UI implementation such as uwu/shelter#39 as the implementation refers to default Discord button (which use the variable). Is not using --button-filled-brand-text variable intended here? I'm happy to create PR for this issue if the variable is actually should be used.