Add support for the new UI

[raggesilver]

There are a few parts of the new UI that don't look right with this theme.

1. There is no padding on the right side of the header bar:

See the default theme for comparison.

2. The contrast for some UI buttons is extremely poor

See the default theme for comparison.

[papey]

Don't know it's only related to Dawn but #10

[keriefie]

When I use dawn on the New UI, the white icons like the Build (hammer) and the More Actions (three dots) are barely visible.

The grey on purple is also relatively unpleasant.