fix(vue3): fullscreen mode in Vue 3 container

[ShGKme]

☑️ Resolves

• Fullscreen layout due to mounting inside #content instead of replacing it

🖌️ UI Checklist

🖼️ Screenshots / Screencasts

🏚️ Before	🏡 After

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[DorraJaouad]

style

	// Fix fullscreen black bar on top
	&:fullscreen {
		padding-top: 0;

		:deep(.app-sidebar) {
			height: 100vh !important;
		}
	}

may not be used

[ShGKme]

The problem with an empty space (reproducible only with the default theme) fixed by applying styles to the :root

[Antreesy]

Tested