The panel was styled with light-theme CSS-var fallbacks that render wrong on
the editor's dark (#2d2d2d) property dialog:
- "Add files" button used `var(--surface, #f6f6f6)` + light border, so it
rendered a washed-out light-gray box that looked broken. Restyle it as a
primary action like `.rotate-button` (solid #007acc, white text, hover lift).
- Section divider and secondary text used light fallbacks (#e2e2e2 / #777);
switch to the dialog's dark values (#444 border, #aaa text).
Cosmetic only.
878e84e98a