Add a spinner for image captioning button

extensions/caption/style.css

@@ -32,4 +32,16 @@
     .mes img.img_extra {
         max-width: 100%;
     }
+}
+
+.spin {
+    animation-name: spin;
+    animation-duration: 2000ms;
+    animation-iteration-count: infinite;
+    animation-timing-function: linear;
+}
+
+@keyframes spin {
+    from {transform:rotate(0deg);}
+    to {transform:rotate(360deg);}
 }