:enabled, :disabled
<style>
input:enabled{ background-color:#fff; border:#333 1px solid; }
input:disabled{ background-color:#CCC; border:#333 1px solid;; }
</style>
<input type="text" name="tx1" value="caja de texto habilitada" size="25"/>
<input type="text" name="tx2" value="caja de texto deshabilitada" size="25"/>
:checked
<style>
input [type="checkbox"]{ margin-right:1em; outline:#333 1px dashed; }
input [type="checkbox"]:checked{ outline:#0C3 1px solid; }
</style>
<label for="cb1">Senderismo</label><input type="checkbox" name="cb1" />
<label for="cb2">Libros</label><input type="checkbox" name="cb2" checked="checked"/>
<label for="cb3">Deportes</label><input type="checkbox" name="cb3"/>