<style>
:indeterminate ~ .cs-valid-tips::before{content:"您尚未选择任何选项"; color: red; font-size: 87.5%;}
</style>
<input type="radio" id="radio1" name="raido">
<label for="radio1">单选项1</label>
<input type="radio" id="radio2" name="raido">
<label for="radio2">单选项2</label>
<input type="radio" id="radio3" name="raido">
<label for="radio3">单选项3</label>
<p class="cs-valid-tips"></p>
| 