enlarge the header sidebar ?

Hello, I would like to enlarge the header sidebar. Changes in the css is not displayed. With Firebug it works.

ex, I would like change “height: 60px;” by “height: 300px;”

#sidebar-header {
	overflow: hidden;
	float: right;
	width: 49.78723404255319%;	/* 468 / 940 = 0.4978723404255319 */
	height: 60px;
	margin-bottom: 20px;
}

it does not work:

#sidebar-header {
	overflow: hidden;
	float: right;
	width: 49.78723404255319%;	/* 468 / 940 = 0.4978723404255319 */
	height: 300px;
	margin-bottom: 20px;
}

Thank’s for help, I can not do..