Add custom size offsets for rendering and custom delimiter styles

This would look like a 'custom' option in each dropdown, which upon selection, spawns

1. for sizes, a +- dropdown, and a textbox where the user can specify the size diff as an integer
2. for delimiters, two custom textboxes for start and end

Feedback:

Your automatic makes formulas too small compared to text. See attached 02-Automatic.png.
How to get around the problem, I know. For example, I can increase text font size, select auto, render formulas, and then decrease the font size. But tools are made to make things easier.
Therefore, I propose to add the ability to set the custom font size of formulas - absolute (16 or 18...) or relative (auto -2, -1, 0, +1, +2)
Also I propose to add Delimiter Style $...$ or custom Delimiter Style.

The issue names no files or tests; begin by finding the size and delimiter dropdown implementations and the rendering path they configure. Confirm that custom size controls support relative integer offsets and that custom delimiter controls accept start and end text, then verify both selections affect rendered output.