Update color variable (#1028)

Author: tcbegley

static/loading.css

@@ -11,7 +11,7 @@
   display: inline-block;
   width: 2rem;
   height: 2rem;
-  color: var(--secondary);
+  color: var(--bs-secondary);
   vertical-align: text-bottom;
   border: 0.25em solid currentColor;
   border-right-color: transparent;