Tous les trucs qu'on utilise le plus souvent.
.sr-only
.img-fluid
<img src="..." class="img-fluid" alt="Responsive image">
No grid classes are necessary for full-width elements.
.offset-md-3
.hidden-sm-down
.hidden-xl-up
.push-md-3
.pull-md-9
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Whenever you need to, be sure to use margin utilities to keep things nice and tidy.