Increase Font size of Date Header in Gantt View

Hi - New user, using OP to generate a Gantt for a grant application which often needs resizing to fit a specific format, which in turn often requires quite large fonts to begin with (so tasks, etc are still readable when resized).

The documentation is generally great, and I’ve worked most things out except this. When I increase the font size in Gantt view the date header at the top does not increase in size, and there seems no way to select it, in order to apply font changes to it. This feels like a simple problem that I’m missing something obvious for. Any help appreciated!