* Make fileheader sticky #12552
* Remove sticky filenames when width is 480px or less
On mobile phone sticky filename is hidden due to the combination
of many possible widths and lengths.
* Fix text color for .markdown-info
* Fix visual of sticky diff box on 480px or less
- Hide arrow for select buttons.
- Fix changes, additions and deletions.
With flexbox they look very broken.
This commit hides some words to, so the result is:
"123 changed files 987 additions 456 deletions"
- center text in buttons
Co-authored-by: zeripath <art27@cantab.net>
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