SO fiddle

Test Fiddle mainly for SO Questions

by Nick Craver

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/overcast/jquery-ui.css">
<input type="text" class="error" />

CSS

input[type="text"]:focus{background:blue;}
input[type="text"].error{background:red;}