Bug 289800 – -webkit-backdrop-filter ignores css variables

• Status: NEW
• Component: CSS

--blur-size: 8px;
    --blur: blur(var(--blur-size));

    -webkit-filter: var(--blur); /* works */
    -webkit-filter: blur(var(--blur-size)); /* works */

    -webkit-backdrop-filter: blur(8px); /* works */
    -webkit-backdrop-filter: var(--blur); /* dont work */
    -webkit-backdrop-filter: blur(var(--blur-size)); /* dont work */

in devtools -webkit-backdrop-filter is marked as applied and the value of variables is displayed, but there is no blur effect itself. 
-webkit-filter works properly with the same variables.
Chromium, FIrefox, etc does not have this problem.
Bug persist in Tauri 2.0 app built with webkitgtk_4_1 version 2.46.6 from nixos unstable
Same app built on windows does not have this bug

[Radar WebKit Bug Importer]

<rdar://problem/147591500>