Mouse cursor is hard to see

[Pelle-Reimers]

Pixelorama version:
v0.9.1-stable

OS/device including version:
Ubuntu 20.04

Issue description:
The mouse cursor is really hard to see, at least on my screen. (See screenshot for a "find waldo"-challenge.)

(Waldo-spoiler: The cursor is in the blue are below the canvas, to the right.)

Steps to reproduce:

• Have a screen size of 3840 × 2160.
• Set the Pixelorama display size to 2.5. (Edit → Preferences, tab Interface, Display size =2.5, press apply)
• Set the theme to Light. (Edit → Preferences, tab Interface, under Theme select Light)
• Have a hard time clicking around because you can't see the cursor. (To help with this step I recommending acquiring myopia 🤓)

Possible causes:

• The light theme clashes badly with the white crosshair.
• The cursor doesn't scale with display size.
• The crosshair is used on all UI, not only on the canvas.