表单的mdbootstrap标签无法正常工作

Question

我正在mdbootstrap的帮助下在Angular中设计一个表单。我无法更改标签的字体大小。下面是我的代码：

<div class="card w-50 p-3">
<h1 class="card-header">Login <i class="material-icons">
    lock_open
    </i></h1>
    <div class="card-body">
  <form [formGroup] = "userForm" (ngSubmit) = "onSubmit()">
      <div class="md-form">
        <label>
          E-mail &nbsp;&nbsp;<i class="material-icons">
            mail_outline
            </i>
          </label><br>
        <input type="email" formControlName = "email"><br><br><br>

      </div>
      <div class="md-form">
          <label>Password &nbsp;<i class="material-icons">
              visibility_off
              </i></label><br>
          <input type="password" formControlName = "password"><br><br><br>
      </div>
  </form>
</div>
</div>

这是我的表单的样子：