FYI, I added very basic Code Mirror support to my theme if anyone was looking for it.
/* code mirror */
/* background and base color */
.cm-s-material-darker.CodeMirror {
background-color: var(--black) !important;
color: var(--light-grey) !important
}
/* lists */
.cm-s-material-darker .cm-variable-2 {
color: var(--light-grey) !important
}
/* internal links */
.cm-s-material-darker .cm-string {
color: var(--primary) !important
}
/* headers */
.cm-header-1, .cm-header-2, .cm-header-3, .cm-header-4 {
color: var(--dark-white) !important
}