add header-line face

[kaiwk]

header-line inherit from mode-line by default, so modifing mode-line has side effects to header-line, see:

• https://github.com/kiennq/emacs-mini-modeline/issues/39#issue-686382474
• https://github.com/bbatsov/zenburn-emacs/blob/6ca85d248468639650fcce2c2d13c46c6e99ded3/zenburn-theme.el#L177

[ianyepan]

Thanks for pointing this out @kaiwk! Could you provide one example where header-line is used, and also if it's bad that we keep it the same as mode-line? Just trying to decide if I should give header-line its own face declaration.

[kaiwk]

AFAIK, any mode derived from tabulated-list-mode will use header-line to show table head, such as package-menu-mode(triggered by list-package).

I think in most case it will be fine, except when someone want to heavily customize mode-line, for example, set mode line height to '0.1'. it seems many other themes tend to set header-line:

• monokai: https://github.com/oneKelvinSmith/monokai-emacs/blob/4281fc13dadef98942c8d43024de024f2392fec5/monokai-theme.el#L603
• cyberpunk: https://github.com/n3mo/cyberpunk-theme.el/blob/cbd0d7193e69ff9e98262eb06aee3d27667ff5f5/cyberpunk-theme.el#L125
• leuven: https://github.com/fniessen/emacs-leuven-theme/blob/a116202c82613c087440d2e8a6a504b08f1862ce/leuven-theme.el#L213

[ianyepan]

I see. Let me try to declare header-line separately so users' customization of mode-line won't affect header-line.

[ianyepan]

Hi @kaiwk, I just fixed it in the following commit: https://github.com/ianpan870102/vscode-dark-plus-emacs-theme/commit/1e694e1704e6bf55726040953ed5cf703f02c16d Closing issue for now, and thx again for bringing this up 👍