Blog and in the entries to full width

Hi there,

You can use the after header hook:
http://demo.generatepress.com/hook-locations/
https://docs.generatepress.com/article/hooks-overview/

With conditional tag like this and check execute PHP

<?php if ( is_single() || is_home() ) : ?>
     <div class="header_banner">
        Your stuff in here
    </div>
<?php endif; ?> 

Then style it with some CSS:

.header_banner {
    background-color: #000000;
    color: #ffffff;
    font-size: 20px;
    text-align: center;
}

Thank you very much Leo
Perfect

Glad I could help!