Review UI refinements: separator styling and header layout #1065

Job	Run time
test	50s
build	1m 22s
install-script-smoke (ubuntu-latest, plannotator-linux-x64)	20s
smoke-binaries (ubuntu-latest, plannotator-linux-x64)	28s
smoke-binaries (windows-latest, plannotator-win32-x64.exe)	41s
npm-publish	54s
attest	0s
release	0s
	4m 35s

Provide feedback