[Bug]: Light image viewer

[bertob]

Describe the bug

When opening an image the image viewer is no longer dark, which is not in line with the HIG.

It seems that this was motivated because the floating buttons were not visible enough (?), but it's definitely not a good solution. For an app like this keyboard shortcuts / Ctrl + scroll / pinch to zoom would probably be enough to be able to just drop the explicit zoom buttons.

Steps To Reproduce

1. Open an image in the timeline

Logs and/or Screenshots

Instance Backend

Mastodon

Operating System

Fedora 38

Package

Flatpak

Troubleshooting information

os: GNOME 44 (Flatpak runtime)
prefix: /app
flatpak: true
version: 0.4.0 (production)
gtk: 4.10.3 (4.10.3)
libadwaita: 1.3.2 (1.3.2)
libsoup: 3.4.2 (3.4.2)
libgtksourceview: 5.8.0 (5.8.0)

Additional Context

No response

[GeopJr]

Sounds good to me!

However, that issue will probably come up again for the pagination buttons, should they also be removed? (pagination also works with the arrow keys and the carousel gestures)

note to self: add Ctrl+, Ctrl- & Ctrl + mouse wheel shortcuts