docs(accordion): fix a11y error

Co-authored-by: Steven Spriggs <[email protected]>

Author: bennypowers

elements/pfe-accordion/demo/pfe-accordion.html

@@ -253,7 +253,7 @@ <h3>Reprehenderit cupidatat labore?</h3>
     </pfe-accordion>
   </pfe-band>
 
-  <pfe-band class="custom-styles" full-width id="custom">
+  <pfe-band class="custom-styles" full-width id="custom-band">
     <h2>Custom styles</h2>
     <pfe-accordion id="custom">
       <pfe-accordion-header>