Issues with CSS StyleSheets on Hotspot pages

I have edited my hotspot pages so that they use a .css stylesheet rather than embedding the style in tags in each page.

Setup:
RouterOS 4.11 on x86.
Hotspot uses HTTP-CHAP only
all html pages/stylesheets are in the /hotspot root directory
Each page has an entry in the tag like this:
I haven’t modified any of the HIDDEN fields


When I hit login.html for the first time, the page is displayed correctly.
If an incorrect username/password is entered and login.html is displayed again with the error message, my custom style is gone!

I’ve also tried href=“style.css” instead of href=“/style.css” but that doesn’t work either.

Does anyone have their hotspot pages using css stylesheets? Can they share their html to help me out?