IE6 не поддерживает селекторы атрибутов.
/* So, this would work in IE6: */
input { font-weight: bold; }
/* But IE6 won’t understand this: */
input[type="text"] { font-weight: bold; }
/* If you combine the two, IE6 still won’t understand it!
It will drop the entire rule set, and it won’t apply any of its styles.
*/
input, input[type="text"] { font-weight: bold; }