<div>
  <div aria-hidden="false" role="dialog" class="slds-modal slds-fade-in-open">
    <div class="slds-modal__container">
      <div class="slds-modal__header">
        <h2 class="slds-text-heading--medium">Modal Header</h2>
        <button class="slds-button slds-button--icon-inverse slds-modal__close">
          <svg aria-hidden="true" class="slds-button__icon slds-button__icon--large">
            <use xlink:href="/assets/icons/action-sprite/svg/symbols.svg#close"></use>
          </svg>
          <span class="slds-assistive-text">Close</span>
        </button>
      </div>
      <div class="slds-modal__content">
        <div>
          PLACE YOUR COMPONENT HERE!
        </div>
      </div>
      <div class="slds-modal__footer">
        <div class="slds-x-small-buttons--horizontal">
          <button class="slds-button slds-button--neutral">Cancel</button>
          <button class="slds-button slds-button--neutral slds-button--brand">Save</button>
        </div>
      </div>
    </div>
  </div>
  <div class="slds-backdrop slds-backdrop--open"></div>
</div>

<aura:component implements="force:lightningQuickAction>
//Your modal code goes here
</aura:component>