Header Image Border

Can anyone help me to remove the border to the blue header image above the menu on my page https://jojofield.com/yolo/ please? I have used firebug to try to identify all I can and have added the following to my twenty twelve child theme

.header-image {
	border: 0px !important;
	box-shadow: 0px !important;
	margin-top: 12px !important;
	margin-top: 0.857142857rem !important;
}

But still no joy ??

Thanks