Add first line indent to text, excluding headings

I’ve added a first-line indent using the code text-indent: 2em; but found it adds an indent to all blocks, including headings. Can anyone help me figure out how to exclude headings from applying a first-line indent using CSS?

I am using the Blue Topaz theme and in the Style Settings plugin, there is a way to do this but I don’t remember any hiccups or don’t know whether it might suit you (you could look into the CSS of that theme as well to copy some code).