Refactor z-index values and optimize CSS properties for various seasonal styles; enhance performance with will-change property [skip ci]

Jellyfin.Plugin.Seasonals/Web/oscar.css

@@ -6,7 +6,7 @@
     width: 100%;
     height: 100%;
     pointer-events: none;
-    z-index: 10; /* Behind popups but over background */
+    z-index: 10;
     contain: strict;
     overflow: hidden;
 }
@@ -30,8 +30,9 @@
 }
 
 .oscar-spotlight {
+    will-change: transform;
     position: absolute;
-    top: -10vh;
+    top: 0;
     /* MARK: SPOTLIGHT WIDTH CONFIGURATION */
     /* To adjust bottom width (spread), change 'width' property (e.g., 20vw for narrow, 40vw for wide). */
     /* To adjust top width (origin), modify first two percentages in 'clip-path' (e.g., 48% 0, 52% 0 for a very thin start). */
@@ -42,9 +43,11 @@
     transform-origin: top center;
     animation: spotlight-sweep 12s infinite alternate ease-in-out;
     mix-blend-mode: screen;
+     translate: 0 -10vh;
 }
 
 .oscar-flash {
+    will-change: transform;
     position: absolute;
     width: 10px;
     height: 10px;