Для sweetalert2
пользовательский класс может быть добавлен к нескольким целям:
Swal.fire({
...
customClass: {
container: 'container-class',
popup: 'popup-class',
header: 'header-class',
title: 'title-class',
closeButton: 'close-button-class',
icon: 'icon-class',
image: 'image-class',
content: 'content-class',
input: 'input-class',
actions: 'actions-class',
confirmButton: 'confirm-button-class',
cancelButton: 'cancel-button-class',
footer: 'footer-class'
}
})
Документы: https://sweetalert2.github.io/#custom -класс