zeo.my

Removes WordPress [gallery] embedded CSS and leave [gallery] div element id and class attributes intact.

add_filter( 'gallery_style', 'remove_gallery_style' )
	function remove_gallery_style( $css ) {
		preg_replace( "#<style type=\'text/css\'>(.*?)</style>#s", "", $css );
	}

or

add_filter( 'use_default_gallery_style', '__return_false' );