使用css实现常用的三角效果
项目中三角：
.breadcrumb{
height: 40px;
line-height: 40px;
padding: 0 20px;
border-top: 1px solid #f9c700;
.breadcrumb-title{
text-align: center;
font-size: @fontC;
//通过定义一个伪类after
&:after{
position: absolute;
content: '';
left: 89px;
top: 39px;
border-top: 9px solid @colorM;
//border-left和border-right换成透明色 才能形成三角形 不然是长方形
border-left: 12px solid transparent;
border-right: 12px solid transparent;
//background-color: red;
}
}
详细讲解
实现三角形的方式很多种。比较简单又比较常用的是利用伪类选择器，在网页上也有很多用到这种效果，比如tips信息提示框。下面是自己写的实心三角形，原理其实很简单，代码都能看懂。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
.tri_top, .tri_right, .tri_bottom, .tri_left{
width: 150px;
height: 100px;
background: #CCCCCC;
border-radius: 8px;
margin: 50px 50px;
position: relative;
float: left;
}
.tri_top:before{
content: "";
width: 0px;
height: 0px;
border-left: 10px solid transparent;
border-right: 10px solid transparent;
border-bottom: 10px solid #CCCCCC;
position: absolute;
top: -10px;
left: 65px;
}
.tri_right:before{
content: "";
width: 0px;
height: 0px;
border-top: 10px solid transparent;
border-bottom: 10px solid transparent;
border-left: 10px solid #CCCCCC;
position: absolute;
top: 40px;
left: 150px;
}
.tri_bottom:before{
content: "";
width: 0px;
height: 0px;
border-top: 10px solid #CCCCCC;
border-left: 10px solid transparent;
border-right: 10px solid transparent;
position: absolute;
top: 100px;
left: 70px;
}
.tri_left:before{
content: "";
width: 0px;
height: 0px;
border-top: 10px solid transparent;
border-bottom: 10px solid transparent;
border-right: 10px solid #CCCCCC;
position: absolute;
top: 40px;
left: -10px;
}
</style>
</head>
<body>
<div class="tri_top"></div> <!--三角形在上边-->
<div class="tri_right"></div> <!--三角形在右边-->
<div class="tri_bottom"></div> <!--三角形在底边-->
<div class="tri_left"></div> <!--三角形在左边-->
</body>
</html>
空心三角形该怎样实现呢？看看以下代码，你会发现其实代码跟实心三角形的代码都是差不多。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
.tri_top, .tri_right, .tri_bottom, .tri_left{
width: 150px;
height: 100px;
border: 1px solid #000000;
border-radius: 8px;
margin: 50px 50px;
position: relative;
float: left;
}
.tri_top:before{
content: "";
width: 0px;
height: 0px;
border-left: 15px solid transparent;
border-right: 15px solid transparent;
border-bottom: 15px solid #000000;
position: absolute;
top: -15px;
left: 65px;
}
.tri_top:after{
content: "";
width: 0px;
height: 0px;
border-left: 14px solid transparent;
border-right: 14px solid transparent;
border-bottom: 14px solid #FFFFFF;
position: absolute;
top: -14px;
left: 66px;
}
.tri_right:before{
content: "";
width: 0px;
height: 0px;
border-top: 15px solid transparent;
border-bottom: 15px solid transparent;
border-left: 15px solid #000000;
position: absolute;
top: 39px;
left: 150px;
}
.tri_right:after{
content: "";
width: 0px;
height: 0px;
border-top: 14px solid transparent;
border-bottom: 14px solid transparent;
border-left: 14px solid #FFFFFF;
position: absolute;
top: 40px;
left: 149px;
}
.tri_bottom:before{
content: "";
width: 0px;
height: 0px;
border-top: 15px solid #000000;
border-left: 15px solid transparent;
border-right: 15px solid transparent;
position: absolute;
top: 101px;
left: 69px;
}
.tri_bottom:after{
content: "";
width: 0px;
height: 0px;
border-top: 14px solid #FFFFFF;
border-left: 14px solid transparent;
border-right: 14px solid transparent;
position: absolute;
top: 100px;
left: 70px;
}
.tri_left:before{
content: "";
width: 0px;
height: 0px;
border-top: 15px solid transparent;
border-bottom: 15px solid transparent;
border-right: 15px solid #000000;
position: absolute;
top: 40px;
left: -15px;
}
.tri_left:after{
content: "";
width: 0px;
height: 0px;
border-top: 14px solid transparent;
border-bottom: 14px solid transparent;
border-right: 14px solid #FFFFFF;
position: absolute;
top: 41px;
left: -14px;
}
</style>
</head>
<body>
<div class="tri_top"></div> <!--三角形在上边-->
<div class="tri_right"></div> <!--三角形在右边-->
<div class="tri_bottom"></div> <!--三角形在底边-->
<div class="tri_left"></div> <!--三角形在左边-->
</body>
</html>
写在最后的一个道理： 三角形往哪个方向，那个方向无需设置border，而相反方向设置border颜色，相邻两边的border设为透明。这样就可实现各个方向的三角形。
实心三角形利用CSS中的伪元素· ：before实现，再利用border的transparent属性即可达到效果。而空心三角形是在空心三角形的基础上再加上伪元素：after实现。伪元素：before实现的是一个实心的三角形，伪元素：after实现的是空心的三角形，进而把实心的三角形覆盖，利用绝对定位的top与left的差值绝对了三角形线的粗细而达到如图的效果。