I am using this typoscript in my Page TS Config to add a stylesheet to the RTE:
RTE.default.ignoreMainStyleOverride = 1
RTE.default.contentCSS = fileadmin/templates/css/rte_formats.css
I have used this several times perfectly, however I am working on a new server running TYPO3 7.6.11 and the stylesheet does not link.
If I inspect the RTE the css file is linked there, but the link is broken.
I don't know if it is related but in the filelist area if I open the info window for the css file and click the 'Show' button I get a 404 (the same happens for every file, even though they are working fine on the front end).