[6.x] Asset cropper fixes

[jaygeorge]

Description of the Problem

There were a couple of small issues with the asset cropper:

• Dark mode used the old -dark- syntax
• The toolbar grew and caused overflow on mobile when an aspect ratio was picked

What this PR Does

• Use correct dark color syntax and make the color consistent with the other modals
• Use flex-wrap to avoid overflow on smaller viewports
• Fixes Crop feature does not support dark mode #14159 and Image cropping mobile layout #14154

How to Reproduce

1. Switch to dark mode with the cropping modal open
2. Choose an aspect ratio to bring up more actions on a small viewport to see the overflow