markdown_docs: Fix styling for in-app docs for inline code.
markdown_docs: Fix styling for in-app docs for inline code.

This adds a selector `#message-formatting` which is basically the
modal id to apply night mode style to inline code in the modal.

eeshangarg/zulip,shubhamdhama/zulip,showell/zulip,shubhamdhama/zulip,rht/zulip,kou/zulip,hackerkid/zulip,timabbott/zulip,shubhamdhama/zulip,tommyip/zulip,hackerkid/zulip,andersk/zulip,zulip/zulip,synicalsyntax/zulip,eeshangarg/zulip,showell/zulip,brainwane/zulip,tommyip/zulip,hackerkid/zulip,hackerkid/zulip,timabbott/zulip,andersk/zulip,brainwane/zulip,timabbott/zulip,tommyip/zulip,shubhamdhama/zulip,shubhamdhama/zulip,eeshangarg/zulip,rht/zulip,rishig/zulip,rishig/zulip,showell/zulip,eeshangarg/zulip,hackerkid/zulip,brainwane/zulip,punchagan/zulip,punchagan/zulip,timabbott/zulip,tommyip/zulip,synicalsyntax/zulip,shubhamdhama/zulip,timabbott/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,zulip/zulip,kou/zulip,punchagan/zulip,zulip/zulip,rishig/zulip,eeshangarg/zulip,timabbott/zulip,andersk/zulip,brainwane/zulip,rht/zulip,andersk/zulip,synicalsyntax/zulip,synicalsyntax/zulip,rishig/zulip,kou/zulip,zulip/zulip,synicalsyntax/zulip,synicalsyntax/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,brainwane/zulip,showell/zulip,shubhamdhama/zulip,punchagan/zulip,rht/zulip,rishig/zulip,zulip/zulip,showell/zulip,tommyip/zulip,kou/zulip,tommyip/zulip,synicalsyntax/zulip,punchagan/zulip,zulip/zulip,brainwane/zulip,brainwane/zulip,punchagan/zulip,kou/zulip,punchagan/zulip,andersk/zulip,rht/zulip,showell/zulip,timabbott/zulip,rishig/zulip,showell/zulip,rishig/zulip,zulip/zulip,andersk/zulip,rht/zulip,tommyip/zulip