slds- grid system

 <!-- RESPONSIVE GRID  -->
<div class="slds-grid slds-wrap">
  <div class="slds-col slds-size--1-of-1 slds-small-size--1-of-1 slds-medium-size--1-of-1">     
     
    </div>
</div>




Reference:
        https://trailhead.salesforce.com/en/modules/lightning_design_system/units/lightning-design-system3