cant change header in thesis

So I am struggling with changing thesis header,I have uploaded it here,so you might say header is there,but the problem is,I want header to be in full width,although I have changed the setting in theme control panel,nothing changes. Tried adding this in custom.css

.custom #header_area { background: #fff url(https://mybronchitissymptoms.net/wp-content/uploads/2012/06/header.JPG) no-repeat;
}

How to make that header be from screen to screen( full width). Thank you.