[Feature] Dark Theme on buttons

[shedaniel]

Is your feature request related to a problem? Please describe.
The vanilla button looks alright with dark mode, but a dark theme on buttons (maybe like darker background) would be nice

Describe the solution you'd like

This is a random picture I stole from discord, the button is simply too bright.

Additional context
Another stolen picture:

In this picture, this button is darker, but it is kinda hard to differentiate between active and inactive (enabled or disabled) buttons. The first button is inactive, while the second button is active.

[Juuxel]

Added in LibGui 4.0.