Add blue box-shadow to blue buttons in normal theme

[jolheiser]

Fix #9407

It was mentioned in the issue to use border instead of box-shadow, however semantic (fomantic) used box-shadow so I went with that. arc-green also uses box-shadow.
This CSS more or less copies arc-green but with blue rather than green.
The shade of blue matches the hover color, which is how it used to look afaik (or at the very least is how arc-green operates)

[codecov-io]

Codecov Report

Merging #9573 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #9573      +/-   ##
==========================================
+ Coverage   41.98%   41.98%   +<.01%     
==========================================
  Files         577      577              
  Lines       75970    75970              
==========================================
+ Hits        31893    31898       +5     
+ Misses      40132    40124       -8     
- Partials     3945     3948       +3

Impacted Files	Coverage Δ
modules/log/event.go	64.61% <0%> (-1.03%)	⬇️
models/repo_list.go	74.07% <0%> (+0.92%)	⬆️
models/webhook.go	70.46% <0%> (+1.06%)	⬆️
models/unit.go	67.56% <0%> (+5.4%)	⬆️

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[jolheiser]

Ping LGTM (does it even respond to me?)

EDIT: Yes it does. 🔥