fix: apply flex for AppearancePage colors input

[datlechin]

Fixes #0000

Changes proposed in this pull request:

• Colors input on mobile is broken, apply flex to fix this

Reviewers should focus on:

Screenshot

Before:

After:

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)
• Related core extension PRs: (Remove if irrelevant)

[davwheat]

I haven't tested, but could you show a screenshot of how this looks on desktop with flex? I have a feeling something might mess that up, but I hope I'm wrong.

[datlechin]

@davwheat same as before, on desktop no UI change

Screen.Recording.2022-09-24.at.13.00.40.mov

[luceos]

Thanks @datlechin 💪