your custom css should work, but when I try to use your link though it does not work because the mime type is wrong:
Resource interpreted as Stylesheet but transferred with MIME type text/plain: "https://raw.githubusercontent.com/kwotsin/kwotsin.github.io/master/css/custom.css".
can you just use it as a regular css file in your repo rather than linking to the raw gh data? or paste to the end of that other BS css?