Revert "universal? double backdrop-filters"

This reverts commit 994a7a7f04.

css/common.css

@@ -10,23 +10,13 @@ body {
 }
 
 @supports (backdrop-filter: blur()) {
-    .modal {
+    /*.modal {
         backdrop-filter: blur(2px);
-    }
+    }*/
 
     .modal-content {
         background-color: #2125294d;
-    }
-    
-    .modal-content::before {
-        content: "";
-        position: absolute;
-        top: 0;
-        bottom: 0;
-        left: 0;
-        right: 0;
         backdrop-filter: blur(10px);
-        z-index: -1;
     }
 }