[bug] Tailwind opacity modifiers aren't working

[brendan-kellam]

Describe the bug

https://v3.tailwindcss.com/docs/customizing-colors#using-css-variables

To reproduce

1. Apply a tailwind opacity modifier to a color (e.g., text-primary/80)
2. Observe that the opacity (80%) isn't actually applied

Sourcebot deployment information

Sourcebot version (e.g. v3.0.1): v4.5.1

Additional information

We need to be using just color channels in our globals.css (instead of rgb and hsl functions).
See: https://v3.tailwindcss.com/docs/customizing-colors#using-css-variables