用html5+css3，黑三角是可以展开的，里面是介绍的内容，求大佬教一下怎么做这个可以展开的黑三角

参考，要点击展开需要结合js，帮助到你可以点击采纳支持下哦，谢谢~~

<style>
    .arrowleft {
        display: inline-block;
        width: 0;
        height: 0;
        border-top: 5px solid transparent;
        border-left: 5px solid #000;
        border-bottom: 5px solid transparent;
    }

    div.tab em {
        margin-right: 5px
    }

    div.tab .content {
        display: none
    }

    div.tabopen .content {
        display: block
    }

    div.tabopen .arrowleft {
        display: inline-block;
        width: 0;
        height: 0;
        border-left: 5px solid transparent;
        border-right: 5px solid transparent;
        border-top: 5px solid #000;
        border-bottom: initial;
        vertical-align: middle
    }
</style>
<div>
    <div class="tab tabopen">
        <div class="title"><em class="arrowleft"></em>动作电影</div>
        <div class="content">动作电影详情</div>
    </div>
    <div class="tab">
        <div class="title"><em class="arrowleft"></em>科幻电影</div>
        <div class="content">科幻电影详情</div>
    </div>
    <div class="tab">
        <div class="title"><em class="arrowleft"></em>激情电影</div>
        <div class="content">激情电影详情</div>
    </div>
</div>
<script src="https://g.csdnimg.cn/??lib/jquery/1.12.4/jquery.min.js"></script>
<script>
    $('.tab .title').click(function () { $(this).parent().toggleClass('tabopen').siblings().removeClass('tabopen') })
</script>

<style type="text/css">
.box li {
	list-style-type: none;
}

.box li:before {
	content: "";
	display: inline-block;
	float: left;
    width: 0;
    height: 0;
    border-top: 5px solid transparent;
    border-left: 10px solid #000;
    border-bottom: 5px solid transparent;
}
 
.box li.ck:before {
	transform: rotate(90deg);

}

</style>
</head>
<body>
<ul class="box">
	<li>AAAAA
	</li>
	<li class="ck">BBBBB
	</li>
</ul>

#triangle-right {
    width: 0;
    height: 0;
    border-top: 50px solid transparent;
    border-left: 100px solid red;
    border-bottom: 50px solid transparent;
}





#triangle-bottomleft {
    width: 0;
    height: 0;
    border-bottom: 100px solid red;
    border-right: 100px solid transparent;
}

这两段代码会给你一个启示的，特别是上面的

点击事件，动态切换类名就好

<!DOCTYPE html>
<html lang="en">
 
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .arrow_top {
      width: 0;
      height: 0;
      border-bottom: 30px solid #ff7f0b;
      /* border: 30px solid #ff7f0b; */
      border-left: 30px solid transparent;
      border-right: 30px solid transparent;
      font-size: 0;
      line-height: 0;
    }
 
    .arrow_right {
      width: 0;
      height: 0;
      border-left: 30px solid transparent;
      border-right: 30px solid transparent;
      border-bottom: 30px solid #ff7f0b;
      font-size: 0;
      line-height: 0;
      transform: rotate(90deg);
    }
 
    .arrow_bottom {
      width: 0;
      height: 0;
      border-left: 30px solid transparent;
      border-right: 30px solid transparent;
      border-bottom: 30px solid #ff7f0b;
      font-size: 0;
      line-height: 0;
      transform: rotate(180deg);
    }
 
    .arrow_left {
      width: 0;
      height: 0;
      border-left: 30px solid transparent;
      border-right: 30px solid transparent;
      border-bottom: 30px solid #ff7f0b;
      font-size: 0;
      line-height: 0;
      transform: rotate(270deg);
    }
  </style>
</head>
 
<body>
  <p class="arrow_top"></p> <br>
  <p class="arrow_right"></p><br>
  <p class="arrow_bottom"></p><br>
  <p class="arrow_left"></p><br><br>
</body>
 
</html>

完整代码如下：{如果对你有帮助，可以点给我个采纳吗，谢谢}。
结合jquery实现点击展开功能

<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
	<title> 页面名称 </title>
<style type="text/css">
.box li {
	list-style-type: none;
}

.box li:before {
	content: "";
	display: inline-block;
	float: left;
    width: 0;
    height: 0;
    margin-right: 5px;
    border-top: 7px solid transparent;
    border-left: 7px solid #000;
    border-bottom: 7px solid transparent;
}
.box > li > div {
	display: none;
}
 
.box li.ck:before {
	transform: rotate(90deg);
}
.box > li.ck > div {
	display: block;
}

</style>
<script type="text/javascript" src="http://libs.baidu.com/jquery/1.11.1/jquery.min.js"></script>
</head>
<body>
<ul class="box">
	<li><h5>AAAAA</h5>
		<div>aaaaaa</div>
	</li>
	<li><h5>BBBBB</h5>
		<div>bbbbbb</div>
	</li>
</ul>
<script type="text/javascript">
$(function(){
	$(".box h5").click(function(event){
		$(this).parent().toggleClass("ck");
	});
});
</script>
</body>
</html>

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