Revert "Change to inset"

Safari doesn't support `inset`.

This reverts commit b3706b682e.

res/css/views/elements/_InviteReason.scss

@@ -25,7 +25,10 @@ limitations under the License.
     .mx_InviteReason_view {
         display: none;
         position: absolute;
-        inset: 0;
+        top: 0;
+        bottom: 0;
+        left: 0;
+        right: 0;
         justify-content: center;
         align-items: center;
         cursor: pointer;