doc: fix <code> inside stability boxes
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
tools, doc
Description of change
Mades <code>
backgrounds semi-transparent so they work on all backgrounds. The inline blocks are rendered as #f2f2f2
before and after this change.