fix width of compose input fields (for mailto links)

Currently when using a mailto link (like [mailto:test@example.com](mailto:test@example.com)), the input fields and textarea uses the full width which looks weird on larger screens. This restricts it to use 60%.

On mobile / smaller screens, the inputs and textarea will still use the full width as before, and as designed.

Please review @zinks- @PoPoutdoor @Gomez