<!-- 旧:Bootstrap 4 --><div class="input-group">
<div class="input-group-prepend">
<span class="input-group-text">@</span>
</div>
<input type="text" class="form-control"></div><!-- 新:Bootstrap 5 --><div class="input-group">
<span class="input-group-text">@</span> <!-- 直接放入,无需prepend/append -->
<input type="text" class="form-control"></div>