A less dark dark theme?

### Prerequisites

- [X] I have checked the [Wiki](https://github.com/AdguardTeam/AdGuardHome/wiki) and [Discussions](https://github.com/AdguardTeam/AdGuardHome/discussions) and found no answer

- [X] I have searched other issues and found no duplicates

- [X] I want to request a feature or enhancement and not ask a question

### Description

#### What problem are you trying to solve?
The almost-black color background in the new dark theme is a bit too dark.
Almost black with almost white fonts is too much contrast and actually not that easy on the eyes.

#### Proposed solution
A dark shade of grey is better.
Or, dark shade of blue with white-ish but not pure white letters is better.