JAVASCRIPT

javascript modal close

$('#closemodal').click(function() {
    $('#modalwindow').modal('hide');
});

when modal close event

$("yourid").on('hide.bs.modal', function(){
	// do it here
});

Close Modal

 .close.mat-button {
    position: absolute;
    top: 0;
    right: 0;
    padding: 5px;
    line-height: 14px;
    min-width: auto;
}
   <button class="close" mat-button [mat-dialog-close]="true">X</button>