When using an Aura component with a Quick Action in Salesforce we notice that the width of the modal is small. We can increase the size like this:

<aura:component implements="flexipage:availableForRecordHome,force:hasRecordId,force:lightningQuickAction" 
                controller="MyController"
                access="global" >

   <!-- To increase the width from the default modal used by the quick action-->
    <aura:html tag="style">
        .cuf-content { padding: 0 0rem !important; } 
        .slds-p-around--medium {
        padding: 0rem !important; } 
        .slds-modal__content{ height:unset !important;
        max-height:unset !important; } 
        .slds-modal__container{ max-width:80rem
        !important; width:90% !important; }
    </aura:html>

    <div>
       <!-- your content here -->
    </div>

</aura:component>