Update custom-style.html

src/lib/custom-style.html

@@ -78,7 +78,7 @@
 </html>
 ```
 
-Note, all features of `custom-style` are available when defining styles as part of Polymer elements (e.g. `<style>` elements within `<dom-module>`'s used for defining Polymer elements. The `custom-style` extension should only be used for defining document styles, outside of a custom element's local DOM.
+Note, all features of `custom-style` are available when defining styles as part of Polymer elements, e.g. `<style>` elements within `<dom-module>`'s used for defining Polymer elements. The `custom-style` extension should only be used for defining document styles, outside of a custom element's local DOM.
 
 -->