Simplify loading spinner positioning using inset property

Author: Vianpyro

css/main.css

@@ -59,10 +59,7 @@ header {
 
 #loading-spinner {
     position: fixed;
-    top: 0;
-    left: 0;
-    right: 0;
-    bottom: 0;
+    inset: 0;
     display: flex;
     justify-content: center;
     align-items: center;