Change notification cleaning checkbox color (fixes #511)

app/javascript/flavours/glitch/styles/components/index.scss

@@ -894,7 +894,7 @@
     width: 30px;
     height: 30px;
     font-size: 20px;
-    color: $inverted-text-color;
+    color: $darker-text-color;
     text-shadow: 0 0 5px black;
     display: flex;
     justify-content: center;