how to delete margin-top: 32px !important from twenty twelve
A better way to do this is to add theme support for the admin bar with a callback of "return false", then Wordpress wont ever trigger the _admin_bar_bump_cb
action which is responsible for adding in the margin-top:32px
.
add_theme_support( 'admin-bar', array( 'callback' => '__return_false' ) );