node_modules/material-design-lite/src/textfield/snippets/textfield-expanding.html

<!-- Expandable Textfield -->
<form action="#">
  <div class="mdl-textfield mdl-js-textfield mdl-textfield--expandable">
    <label class="mdl-button mdl-js-button mdl-button--icon" for="sample6">
      <i class="material-icons">search</i>
    </label>
    <div class="mdl-textfield__expandable-holder">
      <input class="mdl-textfield__input" type="text" id="sample6">
      <label class="mdl-textfield__label" for="sample-expandable">Expandable Input</label>
    </div>
  </div>
</form>