The necessity to provide a separate digital document to a service is a common need.
The increase in the size of the upload field in supported browsers is accomplished via vendor prefixing to allow for graceful degradation.
The accept="" attribute in the input is used to restrict the available choices of files allowable via the upload.
<label class="label venus " for="file" id="upload">
Upload a file
<br/>
<span class="label__description pluto">File types accepted are .xls and .xlsx</span>
</label>
<input type="file" accept=".xls,.xlsx,.pdf" id="file" name="file" class="input input--upload" aria-describedby="upload" />
{
"upload_accepts": ".xls,.xlsx,.pdf"
}