fix color contrast on toggles

frontend/src/metabase/components/Toggle.css

@@ -7,7 +7,7 @@
   height: 24px;
   border-radius: 99px;
   border: 1px solid var(--color-border);
-  background-color: var(--color-bg-light);
+  background-color: var(--color-bg-medium);
   transition: all 0.3s;
 }
 
@@ -23,7 +23,7 @@
   position: absolute;
   top: 1px;
   left: 1px;
-  background-color: var(--color-bg-medium);
+  background-color: white;
   transition: all 0.3s;
 }