How can I make the editor font bolder?

[CalebJohn]

I'm not sure exactly (aside from looking at the source code) but @dpoulton had some instructions that I think are probably what you want.

Custom stylesheets

@DominicDesbiens You can also use Help > Toggle development tools from the Joplin menu and: Click on the element inspector - Marked (1) in the below picture (click to expand) Point it at the item of interest in the rendered note - (2) See its full element name in the pop-up - (3) Look at it in detail in the main tool window - (4) [2020-02-03 17_25_06-Window]