interesting, i tried to apply the inline style to controls div instead of the html element and it doesnt work, you can see the values changing like it does on the html elmeent but it doesnt change the rendering at all

clintfisher · clintfisher · commit 38d698313ed4 · 2018-06-12T19:25:42.000-07:00
diff --git a/03 - CSS Variables/index-START.html b/03 - CSS Variables/index-START.html
@@ -62,6 +62,7 @@ <h2>Update CSS Variables with <span class='hl'>JS</span></h2>
 
 
   <script>
+    const controls = document.querySelector('.controls')
     const inputs = document.querySelectorAll('.controls input');
     console.log('inputs: ', inputs);
     function handleUpdate () {
@@ -70,6 +71,7 @@ <h2>Update CSS Variables with <span class='hl'>JS</span></h2>
       // 'undefined'
       const suffix = this.dataset.sizing || '';
       document.documentElement.style.setProperty(`--${this.name}`, this.value + suffix);
+      controls.style.setProperty(`--${this.name}`, this.value + suffix);
       // console.log('suffix: ', suffix);
       // console.log('name: ', this.name);
     };
