Tvheadend

Use the zoom function of your Web brower. Works fine in Chrome and Firefox.

Black theme have a bigger font

The default font is too small (and that should be changed and possibly made configurable), but indeed "access" theme has a bigger font (and is better looking IMO). Also zooming works as a workaround.

If you use CTRL+mousewheel to zoom, you need to be focused at a right part of the UI (if your mouse is hovering over EPG, it won't work, for example). CTRL+"+" will always work.

Anyone can apply a workaround, this isn't what this feature request is about. I am aware of the alternatives. The ability to adjust the font size to the users preference based on eyesight and or screen resolution would prove helpful.