<div class="slds-is-relative slds-col slds-size_5-of-12 slds-float_right ">
    <section if:true={opt.checked} class="slds-popover slds-nubbin_left" role="dialog">
        <div class="slds-popover__body">
            <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et
                dolore magna aliqua.</p>
        </div>
    </section>
</div>

.slds-popover.slds-nubbin_left{
    position: absolute;
    left:0rem;
    top:-1.3rem;
}