<!DOCTYPE html> <html> <style> input { color: green; } input.notdefault:default { color: red; } input.default:not(:default) { color: red; } </style> <body> <input type="submit" form="one" class="notdefault"> <form id="one"> <input type="submit" class="default"> </form> <script> document.body.offsetWidth; document.getElementById("one").id = "two"; </script> </body> </html>