CODE EXAMPLE FOR CSS

bootstrap4 file upload

<div class="input-group">
  <div class="input-group-prepend">
    <span class="input-group-text" id="inputGroupFileAddon01">Upload</span>
  </div>
  <div class="custom-file">
    <input type="file" class="custom-file-input" id="inputGroupFile01"
      aria-describedby="inputGroupFileAddon01">
    <label class="custom-file-label" for="inputGroupFile01">Choose file</label>
  </div>
</div>