Ran most of the Less files through the Less compiler and Prettier and
then followed up with a round of manual fixes.
The Less compiler had unfortunately stripped all `//` style comments
that I had to restore (It did preserve `/* */` comments). Other fixes
include duplicate selector removal which were revealed after the
transpilation and which weren't caught by stylelint before but now are.
Fixes: https://github.com/go-gitea/gitea/issues/15565
The CSS styles in Gitea themes are out-of-sync of Chroma's styles.
This PR introduces a `chroma-style-diff.go` tool to compare the diff.
The missing CSS styles have been added manually. They are left as empty
to reduce arguments because there was no color for them before.
And this PR fixes #22348, with just 2 lines changed: `.chroma .kt & .n`,
these colors are taken from GitHub.
It's good enough for #22348
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Co-authored-by: silverwind <me@silverwind.io>
