When you're in learning mode, you aren't just searching for specific things in the text. One, or at least myself, is scrutinizing every line to figure out what the heck is going on and where everything is. So it's understandable you want better formatting.

My advice is to save the original as plain text, like everyone else recommends. However, if you only log a day or a few hours at a time, then you can pull your file into Libreoffice or your favorite word processor, save it as a different html file, then change the default font color and background text to whatever you like. You can then use a browser to open it up and read through it slowly without making your eyes bleed. I mention Libre office instead of MS office because it's free to obtain.

It's also possible to code a format tool, or do various complicated things in Cmud, but maybe way more fun to focus on exploring first :)