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

<!-- Numeric Textfield -->
<form action="#">
  <div class="mdl-textfield mdl-js-textfield">
    <input class="mdl-textfield__input" type="text" pattern="-?[0-9]*(\.[0-9]+)?" id="sample2">
    <label class="mdl-textfield__label" for="sample2">Number...</label>
    <span class="mdl-textfield__error">Input is not a number!</span>
  </div>
</form>