Add header background with amp-plugin

Hi,

I found a code in order to add a header background to my amp version, first I want to know if this code is correct, second where to add it. Thank you
header.amp-wp-header {
padding: 12px 0;
background: #000;
}
header.amp-wp-header a {
background-image: url( 'https://lowtechnation.com/wp-content/uploads/2020/05/Illustration_sans_titre-site-4.jpg' )!important;
background-repeat: no-repeat;
background-size: contain;
display: block;
height: 28px;
width: 94px;
margin: 0 auto;
text-indent: -9999px;
}

Do I have to resize my background image before ?

I found thank you


.td-header-wrap {
background-image: url( 'XXXXXXXX' );
background-size: cover;
background-repeat: no-repeat;
background-position: center;
}