我正在使用引导卡“ Cards”构建专辑，我试图做两件事：
1）卡片是否可以完全扩展为小尺寸的屏幕col-sm-12？
2）隐藏屏幕较小的元素.d-sm-none .d-md-block？
第19和86行的问题
答案 0 :(得分：1)
遵循这些指南
style="width: 18rem;"并删除<div class="mb-3">包装器mb-3添加到下一个div包装器类=“ col-sm-12 col-md-3 mb-3”“，扩展卡应该可以工作。col-sm-12替换为col-12 答案 1 :(得分：1)
如果要使用手机屏幕，则应使用col-12，col-sm-12用于风景手机；并且在类名中包含点，它应该是d-none或d-md-block ... HTML结构上还存在其他一些问题；列应为row的直接子代；您在row和列之间有另一个div
在网格布局中，必须将内容放置在列中，并且只有列可以是行的直接子代。
我对row和columns的结构进行了一些修复；我还删除了卡上设置的宽度，以防止它们使用整个宽度。还修复了您正在使用的显示类名，请查看
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet" />
<div class="container">
<div class="row">
<div class="col-12 col-md-3">
<div class="card mb-3">
<img class="card-img-top" data-src="holder.js/100px225?theme=thumb&bg=55595c&fg=eceeef&text=Thumbnail" alt="Thumbnail [100%x225]" style="height: 225px; width: 100%; display: block;" src="data:image/svg+xml;charset=UTF-8,%3Csvg%20width%3D%22348%22%20height%3D%22225%22%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20348%20225%22%20preserveAspectRatio%3D%22none%22%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%3E%23holder_169b97cc54a%20text%20%7B%20fill%3A%23eceeef%3Bfont-weight%3Abold%3Bfont-family%3AArial%2C%20Helvetica%2C%20Open%20Sans%2C%20sans-serif%2C%20monospace%3Bfont-size%3A17pt%20%7D%20%3C%2Fstyle%3E%3C%2Fdefs%3E%3Cg%20id%3D%22holder_169b97cc54a%22%3E%3Crect%20width%3D%22348%22%20height%3D%22225%22%20fill%3D%22%2355595c%22%3E%3C%2Frect%3E%3Cg%3E%3Ctext%20x%3D%22116.71875%22%20y%3D%22120.15%22%3EThumbnail%3C%2Ftext%3E%3C%2Fg%3E%3C%2Fg%3E%3C%2Fsvg%3E"
data-holder-rendered="true" />
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">
Some quick example text to build on the card title and make up the bulk of the card's content.
</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-sm-12 col-md-3">
<div class="card mb-3">
<img class="card-img-top" data-src="holder.js/100px225?theme=thumb&bg=55595c&fg=eceeef&text=Thumbnail" alt="Thumbnail [100%x225]" style="height: 225px; width: 100%; display: block;" src="data:image/svg+xml;charset=UTF-8,%3Csvg%20width%3D%22348%22%20height%3D%22225%22%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20348%20225%22%20preserveAspectRatio%3D%22none%22%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%3E%23holder_169b97cc54a%20text%20%7B%20fill%3A%23eceeef%3Bfont-weight%3Abold%3Bfont-family%3AArial%2C%20Helvetica%2C%20Open%20Sans%2C%20sans-serif%2C%20monospace%3Bfont-size%3A17pt%20%7D%20%3C%2Fstyle%3E%3C%2Fdefs%3E%3Cg%20id%3D%22holder_169b97cc54a%22%3E%3Crect%20width%3D%22348%22%20height%3D%22225%22%20fill%3D%22%2355595c%22%3E%3C%2Frect%3E%3Cg%3E%3Ctext%20x%3D%22116.71875%22%20y%3D%22120.15%22%3EThumbnail%3C%2Ftext%3E%3C%2Fg%3E%3C%2Fg%3E%3C%2Fsvg%3E"
data-holder-rendered="true" />
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">
Some quick example text to build on the card title and make up the bulk of the card's content.
</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-sm-12 col-md-3">
<div class="card mb-3">
<img class="card-img-top" data-src="holder.js/100px225?theme=thumb&bg=55595c&fg=eceeef&text=Thumbnail" alt="Thumbnail [100%x225]" style="height: 225px; width: 100%; display: block;" src="data:image/svg+xml;charset=UTF-8,%3Csvg%20width%3D%22348%22%20height%3D%22225%22%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20348%20225%22%20preserveAspectRatio%3D%22none%22%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%3E%23holder_169b97cc54a%20text%20%7B%20fill%3A%23eceeef%3Bfont-weight%3Abold%3Bfont-family%3AArial%2C%20Helvetica%2C%20Open%20Sans%2C%20sans-serif%2C%20monospace%3Bfont-size%3A17pt%20%7D%20%3C%2Fstyle%3E%3C%2Fdefs%3E%3Cg%20id%3D%22holder_169b97cc54a%22%3E%3Crect%20width%3D%22348%22%20height%3D%22225%22%20fill%3D%22%2355595c%22%3E%3C%2Frect%3E%3Cg%3E%3Ctext%20x%3D%22116.71875%22%20y%3D%22120.15%22%3EThumbnail%3C%2Ftext%3E%3C%2Fg%3E%3C%2Fg%3E%3C%2Fsvg%3E"
data-holder-rendered="true" />
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">
Some quick example text to build on the card title and make up the bulk of the card's content.
</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
<div class="col-sm-12 col-md-3 d-none d-md-block">
<div class="card mb-3">
<img class="card-img-top" data-src="holder.js/100px225?theme=thumb&bg=55595c&fg=eceeef&text=Thumbnail" alt="Thumbnail [100%x225]" style="height: 225px; width: 100%; display: block;" src="data:image/svg+xml;charset=UTF-8,%3Csvg%20width%3D%22348%22%20height%3D%22225%22%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%20348%20225%22%20preserveAspectRatio%3D%22none%22%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%3E%23holder_169b97cc54a%20text%20%7B%20fill%3A%23eceeef%3Bfont-weight%3Abold%3Bfont-family%3AArial%2C%20Helvetica%2C%20Open%20Sans%2C%20sans-serif%2C%20monospace%3Bfont-size%3A17pt%20%7D%20%3C%2Fstyle%3E%3C%2Fdefs%3E%3Cg%20id%3D%22holder_169b97cc54a%22%3E%3Crect%20width%3D%22348%22%20height%3D%22225%22%20fill%3D%22%2355595c%22%3E%3C%2Frect%3E%3Cg%3E%3Ctext%20x%3D%22116.71875%22%20y%3D%22120.15%22%3EThumbnail%3C%2Ftext%3E%3C%2Fg%3E%3C%2Fg%3E%3C%2Fsvg%3E"
data-holder-rendered="true" />
<div class="card-body">
<h5 class="card-title">Card title</h5>
<p class="card-text">
Some quick example text to build on the card title and make up the bulk of the card's content.
</p>
<a href="#" class="btn btn-primary">Go somewhere</a>
</div>
</div>
</div>
</div>
</div>