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>
