<form id="form__Login" action="#" method="post">
<label> Part number:
<input pattern="[0-9][a-zA-Z]{3}" name="part" title="A part number is a digit followed by three letters."/>
</label>
<button id="btnSubmit">submit</button>
</form>
<div id="box__content" class="box"></div>
<div id="box__login" class="box"></div>