Optimize CSS related to rendering of fragments

[DeamonDev]

💥 Proposal

I noticed decreased performance while opening (big) fragments in designer since this PR: #6393. The problem occurs on google chrome browser and takes ~6 seconds to open fragment with ~30 nodes. The same fragment is opened on firefox with 0.5sec or even less. I analyzed this using Chrome's profiler and this is caused by using costly CSS selector introduced in mentioned PR:

cursor: draggable ? "grab" : "inherit",
"body:has(&:active) *": {
    cursor: draggable ? "grabbing" : "inherit",
},

I propose to exchange it with sth cheaper.

This Chrome's behavior is probably caused by the fact it uses single-threaded engine for computing layouts.