Hi, I just had a check and the problem is that you saved the html pages instead of the raw text from the Github pages that you saw the stylesheets. In short, when you find a theme (stylesheet file) on a Github page, you need to download the raw text from the page. There’s a Raw button at the top right just above the code, an easy way to get the .less file directly is to do a secondary click on the Raw button and click on the "Save the attached file in “Download” " . Then you will find the .less file in your download folder and then you can move it to the TaskPaper stylesheet folder.
Here are the stylesheets from the page you sent, but in .less file (just have to move them to your stylesheet folder and now it should work) :
StyleSheets.zip (3.7 KB)