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

Jellyfin.Plugin.Seasonals/Web/underwater.css

@@ -35,6 +35,7 @@
 }
 
 .underwater-seaweed {
+    will-change: transform, opacity;
     position: absolute;
     bottom: -1vh;
     font-size: 4rem;
@@ -52,6 +53,7 @@
 }
 
 .underwater-bubble {
+    will-change: transform;
     position: absolute;
     bottom: -5vh;
     border-radius: 50%;
@@ -73,13 +75,13 @@
 }
 
 @keyframes underwater-traverse-up {
-    0% { top: 120vh; }
-    100% { top: -20vh; }
+    0% { top: 0;  translate: 0 120vh; }
+    100% { top: 0;  translate: 0 -20vh; }
 }
 
 @keyframes underwater-traverse-down {
-    0% { top: -20vh; }
-    100% { top: 120vh; }
+    0% { top: 0;  translate: 0 -20vh; }
+    100% { top: 0;  translate: 0 120vh; }
 }
 
 @keyframes underwater-sway-y {
@@ -101,8 +103,9 @@
 }
 
 .underwater-god-rays {
+    will-change: transform;
     position: absolute;
-    top: -50vh;
+    top: 0;
     left: -50vw;
     width: 200vw;
     height: 200vh;
@@ -119,6 +122,7 @@
     transform-origin: top center;
     mix-blend-mode: overlay;
     filter: blur(5px);
+    translate: 0 -50vh;
 }
 
 @keyframes god-rays-sway {