bootstrap4 进度条颜色

默认情况下进度条为蓝色，Bootstrap4 还提供了以下颜色的进度条：

<div class="progress"> <div class="progress-bar bg-success" style="width:40%"></div>

</div> <div class="progress"> <div class="progress-bar bg-info" style="width:50%"></div>

</div> <div class="progress"> <div class="progress-bar bg-warning" style="width:60%"></div>

</div> <div class="progress"> <div class="progress-bar bg-danger" style="width:70%"></div>

</div>