how to make a modal stay center of screen
//add a onclick function to your modal button
<button type="button" class="header__button" data-toggle="modal" data-target="#signUpModal" onclick="modalCenter()">
signup
</button>
//add below function to your scripts
function modalCenter() {
$('#signUpModal').css({
'display': 'flex',
'justify-content': 'center',
'align-items': 'center'
})
}