Add stylesheet to fileinput button

[hoxbro]

Resolves #6475

I don't know if this is the best place to put the CSS in.

Code in the original issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.10%. Comparing base (08f8039) to head (2b1d307).
Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6479       +/-   ##
===========================================
+ Coverage   71.56%   82.10%   +10.53%     
===========================================
  Files         310      312        +2     
  Lines       45996    46048       +52     
===========================================
+ Hits        32917    37807     +4890     
+ Misses      13079     8241     -4838     

Flag	Coverage Δ
ui-tests	36.66% <100.00%> (?)
unitexamples-tests	71.51% <100.00%> (-0.06%)	⬇️

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[monodera]

This change seems to affect the other templates as well and to me these does not look nice.

Without template:

With Material template:

Is it possible to revert it for other templates and make the change specific to the bootstrap template (if it's not an intension)?

[hoxbro]

I'm not sure what you dislike... Is it the height? If so, I don't think this PR changed that behavior. Try commenting out the stylesheets line to see if that restores the behavior.

[monodera]

I'm sorry that I forgot to show the one with Panel 1.3.8 (shown below).

What I don't like for the 1.4 style is the horizontal space from the left edge of the input box to the Browse button. For the Bootstrap theme, the space is equally distributed at the left, top, and bottom, but for (at least) Material and the default templates, the top and bottom paddings are zero. I feel some lack of consistency for the treatment of margins between templates.