Update Frontenddesign

[Bommberk]

Change design:

• maybe darkmode
• font-family
• scrolling by gamelist: If the list isn't at the top, the window should be enlarged;
• ...

[Bommberk]

Idea for a new theme

[Bommberk]

new image is generated

[Bommberk]

The design has been updated, but so far only colors and themes have been added (dark and light mode)
However, these can currently only be changed through System Settings