Custom themes clash with hardcoded button gradients

**Describe the bug** When users create a custom ui theme, they notice that the upvote / add comment buttons display a gradient from a color A to a color B. Color A is modifiable by them, but Color B is not, so they are stuck with an incomplete customization experience. Looking closer to the css rules we can see that for dark mode, the gradient is being generated as such: ```css .btn-primary:is(.dark *) { background: radial-gradient(circle at center right,var(--color-primary-200),var(--color-primary-100)); color: var(--color-zinc-900); } ``` And for light mode: ```css .btn-primary { background: radial-gradient(circle at 20% 0%,var(--color-primary-800),var(--color-primary-900)); color: var(--color-slate-50); border: 1px solid #0000; background-size: 110% 110% !important; } ``` Users are able to customize their `--color-primary-100` and `--color-primary-900` when creating a custom theme, but they can't seem to modify `--color-primary-200` and `--color-primary-800`. **To Reproduce** (if applicable) Steps to reproduce the behavior: 1. Create a custom theme with a `Primary 100` red color. 2. Click on a post, scroll until add comment button is visible. **Expected behavior** Users should be able to modify the `--color-primary-200` and `--color-primary-800` value of their custom themes for dark and light color schemes respectively or have them be generated automatically keeping in mind the custom values set by the user. **Screenshots** <img width="867" height="105" alt="Image" src="https://github.com/user-attachments/assets/be5f2d9b-c910-4120-a57c-943364596e8f" /> **Versions** - Browser: Firefox - Photon version: 2.2.2