Border on a header

HTML & CSS
1

I’m looking to but a black border on my header and i’m wondering if that would be best done on the image itself or put in the code?

2

Either is fine, ut the fewer images, the better, so I’d go for something like

.header {
  border-top: 5px solid #000;
}
3

use this css code:
.header{ border:2px solid #000;}