实体化CSS验证错误未在文本字段下方显示

Question

这是这些表单字段的代码，但是我的验证格式不正确，请检查屏幕截图

<div class="row">
  <div class="col s6 m6 input-field">
    <%= f.text_field :first_name, maxlength: "50", required: true %>
    <%= f.label :first_name, class: "form_label left required_field" %>
  </div>
  <div class="col s6 m6 input-field">
    <%= f.text_field :last_name, class: "validate", maxlength: "50", required: true %>
    <%= f.label :last_name, class: "form_label left required_field" %>
  </div>
</div>