css CSS三角形或胡萝卜。非常适合在以下组合中使用：after，：在伪类之前，用于向菜单的父元素添加指示符。

Posted 2021-05-13

.arrow-up {
	width: 0; 
	height: 0; 
	border-left: 5px solid transparent;
	border-right: 5px solid transparent;
	
	border-bottom: 5px solid black;
}

.arrow-down {
	width: 0; 
	height: 0; 
	border-left: 20px solid transparent;
	border-right: 20px solid transparent;
	
	border-top: 20px solid #f00;
}

.arrow-right {
	width: 0; 
	height: 0; 
	border-top: 60px solid transparent;
	border-bottom: 60px solid transparent;
	
	border-left: 60px solid green;
}

.arrow-left {
	width: 0; 
	height: 0; 
	border-top: 10px solid transparent;
	border-bottom: 10px solid transparent; 
	
	border-right:10px solid blue; 
}