Update ultra.css

Author: Natuworkguy

dist/ultra.css

@@ -2,6 +2,7 @@
     --underline-default-color: red;
 
     --btn-default-color: #0bf00b;
+    --wave-default-color: rgba(255, 255, 255, 0.6);
 
     --tab-default-color: #2196f3;
     --tab-select-color: red;
@@ -98,7 +99,7 @@ button.ultra-button.button-wave .wave-effect {
   border-radius: 50%;
   transform: scale(0);
   animation: ultra-ripple 0.6s linear;
-  background: rgba(255, 255, 255, 0.6);
+  background: var(--wave-default-color, rgba(255, 255, 255, 0.6));
   pointer-events: none;
   z-index: 1;
 }