login nav icon needs to change colour if there's no header background image...

login nav icon needs to change colour if there's no header background image otherwise it will blend in with the buttons background colour on hover

opentech/static_src/src/sass/components/_icon.scss

@@ -37,6 +37,11 @@
         height: 15px;
         margin-right: 5px;
         fill: $color--white;
+        transition: fill $transition;
+
+        .button:hover & {
+            fill: $color--dark-blue;
+        }
 
         .header--has-bg-image & {
             fill: $color--dark-blue;