当文本区域中存在文本时，更改表单提交按钮的样式- Jade / Pug

form(action="/submit" method="post")
  textarea(name="textArea" id="textArea")
  button(type="submit" id="submitButton") Submit

#submitButton {
  background-color: #4CAF50; /* 默认按钮颜色 */
  color: white;
}

#textArea:valid + #submitButton {
  background-color: #008CBA; /* 文本区域中存在文本时的按钮颜色 */
}

html
  head
    style.
      #submitButton {
        background-color: #4CAF50;
        color: white;
      }

      #textArea:valid + #submitButton {
        background-color: #008CBA;
      }
  body
    form(action="/submit" method="post")
      textarea(name="textArea" id="textArea")
      button(type="submit" id="submitButton") Submit