console
<body>
<div class="wrap-only-child">
<div class="wrap">
<span>wrap1-span1</span>
</div>
<div class="wrap">
<div>wrap2-div1</div>
</div>
<div class="wrap">
<span>wrap3-span1</span>
<div>wrap3-div1</div>
</div>
<div class="wrap">
<span>wrap4-span1</span>
<span>wrap4-span2</span>
<div>wrap4-div1</div>
<div>wrap4-div2</div>
</div>
</div>
<div class="wrap-only-of-child">
<div class="wrap">
<span>wrap1-span1</span>
</div>
<div class="wrap">
<div>wrap2-div1</div>
</div>
<div class="wrap">
<span>wrap3-span1</span>
<div>wrap3-div1</div>
</div>
<div class="wrap">
<span>wrap4-span1</span>
<span>wrap4-span2</span>
<div>wrap4-div1</div>
<div>wrap4-div2</div>
</div>
</div>
</body>
body>div {
margin: 24px 0;
}
.wrap-only-child>.wrap,
.wrap-only-of-child>.wrap {
margin: 24px 0;
}
/* 不区分类型-选择.wrap-only-child .wrap下唯一一个子元素 */
.wrap-only-child .wrap :only-child {
background-color: red;
}
/* 区分类型-选择.wrap-only-child .wrap下唯一一个子元素 */
.wrap-only-of-child .wrap :only-of-type {
background-color: red;
}