Yeah, what Greyelf said. 
@CalAl
Greyelf is exactly right. Learning CSS is totally worth it. The effort spent now will pay dividends when you want to do things that Harlowe cannot do on it’s own… or as Greyelf pointed out, work around the limitations of Harlowe.
Just FYI, in the browser, the F12 key or right-clicking and choosing Inspect on a story element will open the Inspector. This exposes all the code in it’s raw HTML form. Once you get used to seeing your stories in this way, CSS becomes easier to implement because CSS requires you to understand the basics of HTML.
Here’s a link to some CSS stuff I figured out with Harlowe… Styling Harlowe. There’s a good part at the beginning showing how the story HTML is organized and where the passage content is, if you find the HTML to be confusing at first. You might gain some more insight from it. Start simple, master changing the link colour, they try your luck with other things. If you see a red link colour at times, it’s most likely from the :active link state which occurs when the mouse button is pressed on a link, but not released.
Good luck and let us know if you have any other questions!
Note: Firefox and Chrome both have similar Inspectors built right in. You don’t need to download or install any extra stuff. Get used to using the Inspector, if you want to start styling your stories like the pros do.