Add button to background image

I have a random background set up on the homepage of my website and I would like to add a button to goes to another page. The other pages have another header.

How can I add this button in a responsive way? Homepage

.img-4 {
        background-image: url(../img/enfant-4.png);
}
.img-5 {
        background-image: url(../img/enfant-5.png);
}
.img-6 {
        background-image: url(../img/enfant-6.png);
}

<div id="entete" >
                        <?php $class = is_front_page() ? 'img-' . rand( 5, 6 ) : 'non-accueil'; ?>
                                        
                        <div class="<?php echo $class; ?>">
                                <?php get_template_part( 'topnav' ); ?>
                        </div>    
</div>

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