There's a suprisingly widespread use of br tags in Moodle to create paragraph spacing. These should be replaced with simple paragraph tags for paragraphs or occasionally ul or li items for lists of text, or simply padding and margin for other spacing effects such as between the icons at the side of sections in courses.

You can see some of the uses by running: grep \<br lang/en/*.php and there's probably more in the code.

It's pretty hard to style br tags across browsers, but something like the below in a theme file should work to make their presence obvious by making them about 10 times larger than usual:

br
{ content: "A" !important;
display: block !important;
margin-bottom: 10em !important;
}