:submit【送信ボタン要素】セレクタ

<form id="form1">
  <p>
    <button>&lt;button&gt;</button>
    <button type="button">&lt;button type="button"&gt;</button>
    <button type="reset">&lt;button type="reset"&gt;</button>
    <button type="submit">&lt;button type="submit"&gt;</button>
  </p>
  <p>
    <input type="button" value='<input type="button">'>
    <input type="reset" value='<input type="reset">'>
    <input type="submit" value='<input type="submit">'>
  </p>
</form>

<script>
$( "#form1 :submit" ).css( "border", "2px red dashed" );
</script>

<form id="form2">
  <p>
    <button>&lt;button&gt;</button>
    <button type="button">&lt;button type="button"&gt;</button>
    <button type="reset">&lt;button type="reset"&gt;</button>
    <button type="submit">&lt;button type="submit"&gt;</button>
  </p>
  <p>
    <input type="button" value='<input type="button">'>
    <input type="reset" value='<input type="reset">'>
    <input type="submit" value='<input type="submit">'>
  </p>
</form>

<script>
$( "#form2 *" ).filter( "input[type='submit'], button[type='submit']" ).css( "border", "2px blue dashed" );
</script>