MFM was defined in three places.
There was ./src/components/status_body/status_body.scss => I moved this to ./src/components/status_content/mfm.scss
There was ./src/components/status_content/status_content.vue => I moved this to ./src/components/status_content/mfm.scss
There's ./static/mfm.css => I kept this as-is
./src/components/status_content/mfm.scss is now being loaded in ./src/components/status_content/status_content.vue
I added a comment in both ./src/components/status_content/mfm.scss and ./static/mfm.css referencing each other
Note that this is just a first step in an overhoal of how MFM is handled. It seemed easier to do this as a first step and then build further on that.