Fix preview indent and status bar LEDs

[vkbo]

Summary:

This PR fixes the em unit calculation in the document preview class. It was using font height instead of font ascent as the base unit. This PR also fixes the High DPI scaling of the Status Bar LEDs.

Related Issue(s):

Closes #1961

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed