Improve One theme contrasts (#20304)

Closes #5334
Closes #15521 

Improve contrast across the board in default One themes. 

We are currently building out some theme tools to make improvements to
contrast and tweaking themes in general easier, so these should continue
to improve over time.

**Light**

Before | After

![CleanShot 2024-11-06 at 11 26
02@2x](https://github.com/user-attachments/assets/2e5d5649-4131-4d42-accc-9bbcf34defeb)

**Dark**
Before | After

![CleanShot 2024-11-06 at 11 30
26@2x](https://github.com/user-attachments/assets/78bc5134-6113-48fd-b026-88e427c631a3)

**Note 1**: there are more improvements to be made, but this should deal
with the most egregious issues.

Release Notes:

- Improved contrast in default One themes