背景颜色
与文本颜色类相似，可以轻松地将元素的背景设置为任意上下文类。背景实用程序不设置color，因此在某些情况下，您将需要使用.text-*。
<div class="p-3 mb-2 bg-primary text-white">.bg-primary</div>
<div class="p-3 mb-2 bg-primary-subtle text-primary-emphasis">.bg-primary-subtle</div>
<div class="p-3 mb-2 bg-secondary text-white">.bg-secondary</div>
<div class="p-3 mb-2 bg-secondary-subtle text-secondary-emphasis">.bg-secondary-subtle</div>
<div class="p-3 mb-2 bg-success text-white">.bg-success</div>
<div class="p-3 mb-2 bg-success-subtle text-success-emphasis">.bg-success-subtle</div>
<div class="p-3 mb-2 bg-danger text-white">.bg-danger</div>
<div class="p-3 mb-2 bg-danger-subtle text-danger-emphasis">.bg-danger-subtle</div>
<div class="p-3 mb-2 bg-warning text-dark">.bg-warning</div>
<div class="p-3 mb-2 bg-warning-subtle text-warning-emphasis">.bg-warning-subtle</div>
<div class="p-3 mb-2 bg-info text-dark">.bg-info</div>
<div class="p-3 mb-2 bg-info-subtle text-info-emphasis">.bg-info-subtle</div>
<div class="p-3 mb-2 bg-light text-dark">.bg-light</div>
<div class="p-3 mb-2 bg-light-subtle text-light-emphasis">.bg-light-subtle</div>
<div class="p-3 mb-2 bg-dark text-white">.bg-dark</div>
<div class="p-3 mb-2 bg-dark-subtle text-dark-emphasis">.bg-dark-subtle</div>
<div class="p-3 mb-2 bg-body-secondary">.bg-body-secondary</div>
<div class="p-3 mb-2 bg-body-tertiary">.bg-body-tertiary</div>
<div class="p-3 mb-2 bg-body text-body">.bg-body</div>
<div class="p-3 mb-2 bg-black text-white">.bg-black</div>
<div class="p-3 mb-2 bg-white text-dark">.bg-white</div>
<div class="p-3 mb-2 bg-transparent text-body">.bg-transparent</div>
背景渐变（Background gradient）
通过添加.bg-gradient-*类，可以将线性渐变作为背景图像添加到背景中。 此渐变从半透明的白色开始，逐渐淡出到底部。
<div class="p-3 mb-2 bg-primary bg-gradient text-white">.bg-primary.bg-gradient</div>
<div class="p-3 mb-2 bg-secondary bg-gradient text-white">.bg-secondary.bg-gradient</div>
<div class="p-3 mb-2 bg-success bg-gradient text-white">.bg-success.bg-gradient</div>
<div class="p-3 mb-2 bg-danger bg-gradient text-white">.bg-danger.bg-gradient</div>
<div class="p-3 mb-2 bg-warning bg-gradient text-dark">.bg-warning.bg-gradient</div>
<div class="p-3 mb-2 bg-info bg-gradient text-white">.bg-info.bg-gradient</div>
<div class="p-3 mb-2 bg-light bg-gradient text-dark">.bg-light.bg-gradient</div>
<div class="p-3 mb-2 bg-dark bg-gradient text-white">.bg-dark.bg-gradient</div>
<div class="p-3 mb-2 bg-black bg-gradient text-white">.bg-black.bg-gradient</div>
