Advance Stylesheet - breaking other styles?

I'm using 8.1.30. I enabled the advanced stylesheet for some testing and noticed that all of my other styles that had been setup were no longer working.

I deleted the stylesheet.css and everything went back to normal.

Am I missing something with using the Advance Stylesheet? I would have assumed it would have no effect on existing styles.

The advanced stylesheet is not parsed or validated in any way by the gateway, and is directly injected as a string into the single stylesheet CSS file that is loaded by the final Perspective page.

You were probably missing a trailing quote or close bracket or something, and so all the styles between the stylesheet and the next quote or bracket in the style classes were ignored or parsed incorrectly.