I'm trying to convert a web page to an extension. All was fine as long as I edited HTML and JS files. Every time I opened the popup, things would be automatically updated, as expected. Now, however, I'm trying to work on the CSS. When I pop up the extension, my changes usually aren't picked up. Instead it will use a seemingly-random past version. There's no way to predict what I'll get, except that it's rare to get the current version. I'm attaching a screenshot with the file opened in a tab and the extension popped up. Notice how the headers are different.

What's going on?



EDIT: I've tried reloading the extension, and I've tried uninstalling and reinstalling it to no avail.

What's the <link> to the css file look like?