Use gradient on `VirtualHorizon` colors #1167

Job	Run time
Test	1m 17s
deploy-blueos-extension	1m 13s
deploy-electron (macos-latest, macos, dmg)	5m 3s
deploy-page	45s
deploy-flatpak	9m 27s
deploy-electron (ubuntu-latest, linux, AppImage)	3m 37s
	21m 22s

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