Fix Obsidian.md blur effect on Safari

[eliyap]

Hi Obsidian Devs, I think it is the closest repo for website bug reports.

Opening obsidian.md on Chrome and Safari, note that the "frosted glass" blur effect is missing in Safari.

This is because the backdrop-filter: blur(5px) property is not supported in Webkit (MDN), but is available as

Implemented with the vendor prefix: -webkit-

When I edit the CSS on Safari to add -webkit-backdrop-filter: blur(5px), it works as intended:

Safari Version: macOS 15.0 Beta 1

[ericaxu]

Added (not live yet), thanks!