Add and fix monitor widget class

internal/assets/static/main.css

@@ -1107,10 +1107,13 @@ kbd:active {
 }
 
 .monitor-site:hover .monitor-site-icon {
-    filter: grayscale(0);
     opacity: 1;
 }
 
+.monitor-site:hover .monitor-site-icon:not(.simple-icon) {
+    filter: grayscale(0);
+}
+
 .monitor-site-status-icon {
     flex-shrink: 0;
     margin-left: auto;