Hi @anacletomarques,
Sorry for the late response because of some unavoidable circumstances. Please go to the Appearance > Customize > Additional CSS and paste the below custom CSS code to remove the black stripe.
.wp-custom-header iframe,
.wp-custom-header video {
height: auto !important;
width: 100% !important;
}
Please let us know if you have any other issues regarding the theme.
Thanks
.
.