Read
the Bootstrap documentation[
^] - you don't show or hide a modal by toggling a CSS class. Instead, you need to invoke the relevant Bootstrap method.
$(".extra").click(function(){
var m = this,
classes = m.className.split(/\s+/);
for (var i = 0; i < classes.length; i++) {
if (classes[i].match(/^modal-/)) {
var modalClass = classes[i];
$(".modal." + modalClass).modal("toggle");
}
}
});
$(".close-modal").click(function(){
$(this).closest(".modal").modal("hide");
});
$(".overlay").click(function(){
$(this).closest(".modal").modal("hide");
});