Enhance CSS animations and performance across seasonal styles; add will-change property for smoother transitions and optimize keyframes. [skip ci]

Jellyfin.Plugin.Seasonals/Web/birthday.css

@@ -8,9 +8,11 @@
     z-index: 9999;
     overflow: hidden;
     contain: strict;
+    contain: layout paint;
 }
 
 .birthday-symbol {
+    will-change: opacity;
     position: fixed;
     top: 0;
     left: 0;
@@ -29,7 +31,7 @@
 }
 
 .birthday-inner {
-    pointer-events: auto; /* Allow hover over the actual item */
+    pointer-events: auto;
     cursor: crosshair;
     display: inline-block;
 }
@@ -138,7 +140,7 @@
         opacity: 1;
     }
     100% {
-        transform: translateY(calc(var(--burst-y) + 150px)); /* Gravity pull downwards */
+        transform: translateY(calc(var(--burst-y) + 150px));
         opacity: 0;
     }
 }