New dark theme and default theme rename

[silverwind]

Feature Description

I think generally we agree that arc-green is a rather unconventional color theme and I don't like it very much. The idea is to make a new default dark theme with light blue primary color and almost-greyscale blue overall color. So I propose:

• Rename gitea theme to gitea-light and migrate existing users
• Rename and update arc-green theme to gitea-dark and migrate existing users

The colors I'd be aiming for are greyscale with a very subtle blue tint. Very similar to this blender theme and to Discord's dark theme, but not as blue as GitHub's dark theme.

Screenshots

[puni9869]

I was waiting for this proposal from long time. FInally the time has come.
It will be included in which milestone 1.21 or .122? I think we should tag this.

[silverwind]

Too late for 1.21, I guess it will be 1.22.

[TheBrokenRail]

Wait, what's wrong with arc-green? I've always thought it looked nice.

[delvh]

As I've understood it:
arc-green is an unconventional dark theme as it is basically the only common dark theme with a large green focus instead of a blue focus.

Ultimately, I'm neutral about which design we choose as we will all be able to adapt to whatever is decided.

[silverwind]

There is at least these issue with current themes:

• Light theme is blue primary, dark theme is green, introducing inconsistency.
• Blue primary is in widespread use, likely because in HTML links are blue and people just went with that.
• Green primary is unconventional. Not saying it couldn't work, but I think we are better off with blue.

[lunny]

We can move arcgreen to a standalone repository so it can be used as external theme

[silverwind]

It would eventually require updates when color variables change, so I think we better kill it completely, or put it up somewhere in a "archived" state with no guarantees.

[JakobDev]

While I personally use a dark theme, I'm in favour of keeping the light theme as default. While currently many sites on the Internet offers a dark theme, the most most will use the light theme as default, so Gitea should also do that. But maybe there's a way to respect prefers-color-scheme, what would even be better.

[silverwind]

DEFAULT_THEME = auto, which is the one that switches with prefers-color-scheme, so that's already taken care of.