simple validation without jquery

HTML

<div>
    <label>
      Please Input Your Name
      <input type="text" id="testVal" />
    </label>
    <input type="button" id="valBtn" value="Validate" onclick="validateTextField();" />
</div>

CSS

label {
    color: #B4886B;
    font-weight: bold;
    display: block;
    width: 150px;
    float: left;
}

label.error {
  color: red;
}