ui: improve mobile review-box sizing

[sapk]

On mobile, review is not possible because the button are on the left out of the screen.
This PR is using viewport unit for sizing the review-box.
(which is supported on most browser now https://caniuse.com/#feat=viewport-units)
This also add a scrollbar if needed to the editor bar.

After

On small screen the review box is kept inside the viewport:

On full screen nothing change:

Before

On small screen the review box is was outside the viewport:

On full screen nothing change:

[guillep2k]

Could you please add a height maximum as well? Since I use a larger DPI setting on my notebook (not mobile), the review buttons always get placed outside the screen (I can scroll down, however):

[sapk]

@guillep2k can we keep that for an other PR ?
I have seen the same problem during testing but it easy to scrolldown to access the button.

[guillep2k]

@guillep2k can we keep that for an other PR ?
I have seen the same problem during testing but it easy to scrolldown to access the button.

OK, I can't do it myself because I don't have enough experience with CSS and its endless list of caveats. 😄

[sapk]

@guillep2k I am not an expert also so I try to limit to the strict minimum even on the css selector to not impact other element

[codecov-io]

Codecov Report

Merging #10297 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #10297      +/-   ##
==========================================
- Coverage   43.73%   43.71%   -0.02%     
==========================================
  Files         585      585              
  Lines       81017    81017              
==========================================
- Hits        35434    35419      -15     
- Misses      41201    41212      +11     
- Partials     4382     4386       +4

Impacted Files	Coverage Δ
modules/indexer/stats/queue.go	62.5% <0%> (-18.75%)	⬇️
modules/indexer/stats/db.go	40.62% <0%> (-18.75%)	⬇️
modules/git/utils.go	65.67% <0%> (-4.48%)	⬇️
services/pull/temp_repo.go	29.05% <0%> (-2.57%)	⬇️
services/pull/patch.go	63.52% <0%> (-2.52%)	⬇️
modules/git/repo.go	46.78% <0%> (-2.3%)	⬇️
models/user.go	49.54% <0%> (ø)	⬆️
models/notification.go	64.13% <0%> (+0.84%)	⬆️
services/pull/pull.go	33.93% <0%> (+1.5%)	⬆️

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