set blue switch color to increase contrast change

Helps the demo page to be more simple to understand, if the change is more easy to see on the screen.

The dark cobalt blue theme is more different to the dark preset colors on mobile devices.

Helps a lot to see that change on click.

index.html

@@ -518,7 +518,7 @@ <h5> Be healthy and happy ! </h5>
  >
 
 <a title=" Lights ON, OFF. "
-   href="javascript:void(0);" onclick="ClassSwitch('html' , 'dark' , 'ColorMode');" 
+   href="javascript:void(0);" onclick="ClassSwitch('html' , 'blue' , 'ColorMode');" 
    style=" color: #111 ; padding: 0.4em 0.1em ; margin: 1px ; text-decoration: none ; float: right ; " 
  >
 🌓<br />