Fix ol.css for some examples

- es2015-custom-element needs css variables declared in :host
- external-map-map still does not work when editing in codesandbox,
  though that neither worked before.

examples/mobile-full-screen.html

@@ -13,7 +13,7 @@ cloak:
     <meta charset="utf-8">
     <meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
     <title>Mobile full screen example</title>
-    <link rel="stylesheet" href="../css/ol.css" type="text/css">
+    <link rel="stylesheet" href="../theme/ol.css" type="text/css">
     <style type="text/css">
       html, body, .map {
         margin: 0;