add ring color

Author: NicolasMontone

client/src/index.css

@@ -26,6 +26,11 @@ a:hover {
   color: #535bf2;
 }
 
+button:focus,
+button:focus-visible {
+  outline: 4px auto -webkit-focus-ring-color;
+}
+
 body {
   margin: 0;
   place-items: center;