情景文本颜色
<p class="text-muted">...</p><p class="text-primary">...</p><p class="text-success">...</p><p class="text-info">...</p><p class="text-warning">...</p><p class="text-danger">...</p>情景背景颜色
<p class="bg-primary">...</p><p class="bg-success">...</p><p class="bg-info">...</p><p class="bg-warning">...</p><p class="bg-danger">...</p>关闭按钮
<button type="button" class="close" aria-label="Close"><span aria-hidden="true">×</span></button>三角符号
<span class="caret"></span>
快速浮动
.pull-left
.pull-right
内容块居中
.center-block
清楚浮动
.clearfix
显示和隐藏
.show
.hidden .sr-only