Bootstrap 4.0 breakpoint indicator
The following HTML with Bootstrap 4.0 will indicate what the current breakpoint is:
<span class="d-inline d-sm-none">XS</span>
<span class="d-none d-sm-inline d-md-none">SM</span>
<span class="d-none d-md-inline d-lg-none">MD</span>
<span class="d-none d-lg-inline d-xl-none">LG</span>
<span class="d-none d-xl-inline">XL</span>