<div class ="container slds-is-relative slds-m-top_medium">
<div class="slds-box slds-theme_default">
<div class="slds-grid slds-gutters slds-wrap">
<div class="slds-col slds-align_absolute-center">
<lightning:input aura:id="file"
type="file"
label=""
name="file"
multiple="false"
accept=".csv"
onchange="{!c.upload}"/>
</div>
</div>
</div>
</div>