I just committed the change to support loading external CSS files in the same way you can load images. The css file has to be stored in the "res" subfolder located at the same level as the stardict dictionary files.

- CSS files must be located in the RES subfolder
- location of css files.PNG (52.25 KiB) Viewed 12155 times
I only tested this with "Oxford English-Chinese dictionary", the only dictionary I have which contains a CSS file:
Before:

- Oxford English-Chinese Stardict dictionary with no css external file handling
- Oxford English-Chinese Stardict dictionary with no css external file handling.PNG (114.64 KiB) Viewed 12155 times
After:

- Oxford English-Chinese Stardict dictionary with css external file handling
- Oxford English-Chinese Stardict dictionary with css external file handling.PNG (98.5 KiB) Viewed 12155 times
As you can see after the fix the CSS is loaded and the text is formatted correctly.
You can compile from source code or wait until next Developer or Early Access build.
Regards