bootstrap 4 spinner overlay code example
Example 1: circlular waiting icon bootstrap
<div class="spinner-border" role="status">
<span class="sr-only">Loading...</span>
</div>
Example 2: bootstrap 4 spinner
<div class="spinner-border spinner-border-sm" role="status">
<span class="sr-only">Loading...</span>
</div>
<div class="spinner-grow spinner-grow-sm" role="status">
<span class="sr-only">Loading...</span>
</div>