<!-- Numeric Textfield with Floating Label -->
<form action="#">
  <div class="mdl-textfield mdl-js-textfield mdl-textfield--floating-label">
    <input class="mdl-textfield__input" type="text" pattern="-?[0-9]*(\.[0-9]+)?" id="sample4">
    <label class="mdl-textfield__label" for="sample4">Number...</label>
    <span class="mdl-textfield__error">Input is not a number!</span>
  </div>
</form>