<div class="modal sidebar">...
</div>
// Centered modal
<div class="modal-dialog modal-dialog-centered">...
</div> // Modal XL
<div class="modal-dialog modal-xl">...
</div> // Modal LG
<div class="modal-dialog modal-lg">...
</div> // Modal SM
<div class="modal-dialog modal-sm">...
</div>
<div class="modal sidebar sidebar-left">...
</div>