refacto(css/pulse-animation): add 'alternate' and edit keyframes

Author: alanb4rt

snippets/css/animations/pulse-animation.md

@@ -3,25 +3,22 @@ title: Pulse Animation
 description: Adds a smooth pulsing animation with opacity and scale effects
 author: AlsoKnownAs-Ax
 tags: animation,pulse,pulse-scale
+contributors: alanb4rt
 ---
 
 ```css
 .pulse {
-    animation: pulse 2s ease-in-out infinite;
+  animation: pulse 1s ease-in-out infinite alternate;
 }
 
 @keyframes pulse {
-  0% {
+  from {
     opacity: 0.5;
     transform: scale(1);
   }
-  50% {
+  to {
     opacity: 1;
     transform: scale(1.05);
   }
-  100% {
-    opacity: 0.5;
-    transform: scale(1);
-  }
 }
 ```