Improve delete button behavior

core/static/core/style.scss

@@ -263,7 +263,13 @@ a:not(.button) {
     &.btn-red {
       background-color: #fc8181;
       color: black;
-      border: #fc8181 1px solid;
+      &:not(:disabled):hover {
+        background-color: darken(#fc8181, 15%);
+      }
+      &:disabled {
+        background-color: lighten(#fc8181, 15%);
+        color: grey;
+      }
     }
 
     i {