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

Jellyfin.Plugin.Seasonals/Web/space.css

@@ -5,12 +5,13 @@
     width: 100vw;
     height: 100vh;
     pointer-events: none;
-    z-index: 9999;
+    z-index: 10;
     overflow: hidden;
     contain: strict;
 }
 
 .space-bg-glow {
+    will-change: transform;
     position: absolute;
     top: 0; left: 0; width: 100vw; height: 100vh;
     background: radial-gradient(circle at 70% 30%, rgba(138, 43, 226, 0.15), transparent 60%),
@@ -33,6 +34,7 @@
 }
 
 .space-shooting-star {
+    will-change: opacity;
     position: absolute;
     width: 250px;
     height: 3px;
@@ -61,11 +63,11 @@
 }
 
 .space-symbol img {
+    will-change: transform;
     width: 6vh;
     height: auto;
     max-width: 60px;
     object-fit: contain;
-    /* Add a slow spin to images */
     animation: space-slow-spin var(--rot-dur, 20s) linear infinite;
 }