原理:
CSS盒模型
一个盒子包括: margin+border+padding+content
上下左右边框交界处出呈现平滑的斜线. 利用这个特点, 通过设置不同的上下左右边框宽度或者颜色可以得到小三角, 小梯形等.
调整宽度大小可以调节三角形形状.
示例1:

#test1 { height:20px; width:20px; border-color:#FF9600 #3366ff #12ad2a #f0eb7a; border-style:solid; border-width:20px; }
示例2:
在上面基础上, 我们把宽高度都设为0时, 会呈现上述的边界斜线.

#test2 { height:0; width:0; overflow: hidden; /* 这里设置overflow, font-size, line-height */ font-size: 0; /*是因为, 虽然宽高度为0, 但在IE6下会具有默认的 */ line-height: 0; /* 字体大小和行高, 导致盒子呈现被撑开的长矩形 */ border-color:#FF9600 #3366ff #12ad2a #f0eb7a; border-style:solid; border-width:20px; }
这时, 其实我们已经看到有上下左右四个三角形了..如果, 我们把4种颜色, 只保留一种颜色, 余下3种颜色设置为透明(或者设置为和背景色相同的颜色), 那不就出现一个小三角了么
示例3:
只保留上面的橙色, 看看

#test3 { height:0; width:0; overflow: hidden; font-size: 0; line-height: 0; border-color:#FF9600 transparent transparent transparent; border-style:solid; border-width:20px; }
可是, IE6下不支持透明啊~~~, 会出现下图的样子
找到一个在IE6下边框透明的文章中找到解决办法, 如下例
示例4:
IE6下, 设置余下三条边的border-style为dashed,,,即可达到透明的效果~ 具体原因可以见参考资料3

#test4 { height:0; width:0; overflow: hidden; font-size: 0; line-height: 0; border-color:#FF9600 transparent transparent transparent; border-style:solid dashed dashed dashed; border-width:20px; }
当然, 在IE6下, 不设置透明, 将其颜色设置为背景色, 使其看不出来也是可以的.
示例5:
上面我们画的小三角的斜边都是依靠原来盒子的边, 还有另外一种形式的小三角, 就是斜边在盒子的对角线上

#test5 { height:0; width:0; overflow: hidden; font-size: 0; line-height: 0; border-color:#FF9600 #3366ff transparent transparent; border-style:solid solid dashed dashed; border-width:40px 40px 0 0 ; }
保留其中一种颜色, 就可以得到斜边在对角线上的三角形了…多个这样的三角形, 通过设置边框大小, 颜色, 拼凑起来可以形成任意形状的三角形.

像这种不规则的三角形, 延伸一下, 放在气泡框上, 就可以省去拼背景图片的麻烦了.

另外, 关于气泡框, 可以使用棱形字符(◆)来实现, 设置其font-size, 颜色和背景色一致, 定位可以使用margin负值和absolute绝对定位来实现, 见示例.
应用之圆角生成
- 应该说是近似圆角,,其实由一个高度非常小的梯形展示出来
- - 上梯形(无上边框,下左右3px宽度, 左右颜色去掉)+矩形+下梯形
-
- 自适应圆角1:
- - 整个rc设置为float: left 或 display: inline-block 分为top,bd,bottom, top中又有两个层rc1和rc2, rc1只设置border-top, 高度为0, 并设置左右margin呈短小的一横线, rc2只设置左右border并且左右margin小于rc1, height为1px, 中间bd设置左右border,不设置左右margin;
- - 不过 IE 6&7 出现 bug:rc在IE6中依然显示为dispaly:block,而IE7中top 和 bottom缩成一坨,不肯扩展开来,而在rc1/rc2/rc3 中插入文字xxx后只能扩展到文字宽度,不能与bd对齐.
- - 见自适应圆角1
- 自适应圆角2
- - 自 Google 系产品的 1px 圆角按钮,,,三层div, 最外层div1正常设置边框宽度1px, 呈现出上下边框线, 中间div2只设置左右边框, 且把左右margin设置成负值, 呈现出圆角处的4个圆点 内层div3同样只设置左右边框, 同时margin上下空出div2的高度, margin左右也设置与div2相同的负值.
- - 见自适应圆角2
其他小问题
- - 透明:
- IE6浏览器不支持transparent透明属性,就border生成三角技术而言,直接设置对应的透明边框的border-style属性为 dotted或是dashed即可解决这一问题,原因是在IE6下, 点线与虚线均以边框宽度为基准,点线长度必须是其宽度的3倍以上(height>=border-width*3),虚线宽长度必须是其宽度的5倍 以上(height>=border-width*5),否则点线和虚线都不会出现.
- - IE6的奇偶bug:
- 如果定位外框高度或是宽度为奇数,则IE6下,绝对定位元素的低定位和右定位会有1像素的误差.所以,尽量保证外框的高度或宽度为偶数值.
- - IE6的空div高度bug:
- IE6下,空div会有莫名的高度,也就是说height:0;不顶用,此时形成的尖角的实际占高于其他浏览器是有差异的.可使用font-size:0; + overflow:hidden;修复此问题.
- - filter: chroma滤镜
- 该属性属性可以设置一个对象中指定的颜色为透明色, 如:
-
border-color: pink; filter: chroma(color=pink);
扩展学习
通过上面给力的文章,我们了解到使用css制作兼容的小三角。
但是日常的小三角哪有这么简单呢?例如我们的一个下拉菜单,里面有一个小三角行的,小三角行有蓝色边框,底色为白色。这就需要运用两个小三角来制作定位了。
通常设置上面的ul相对于上面的li为position:absolute;
这两个的小三角行则是通过伪元素来制作,同时通过一些标签来兼容IE6和IE7的。如:
.header .menu ul:before,.header .menu ul .before { display:inline-block; width:0; height:0; overflow:hidden; line-height:0; font-size:0; vertical-align:middle; border-bottom:7px solid #0088CC; border-top:0 none; border-left:7px dashed transparent; border-right:7px dashed transparent; _color:#FF3FFF; _filter:chroma(color=#FF3FFF); content:""; left:37px; position:absolute; top:-7px } .header .menu ul:after,.header .menu ul .after { display:inline-block; width:0; height:0; overflow:hidden; line-height:0; font-size:0; vertical-align:middle; border-bottom:6px solid #ffffff; border-top:0 none; border-left:6px dashed transparent; border-right:6px dashed transparent; _color:#FF3FFF; _filter:chroma(color=#FF3FFF); content:""; left:38px; position:absolute; top:-6px }
45个值得收藏的CSS形状
1.正方形
#square {
width: 100px;
height: 100px;
background: red;
}
2.长方形
#rectangle {
width: 200px;
height: 100px;
background: red;
}
3.圆形
#circle {
width: 100px;
height: 100px;
background: red;
border-radius: 50%
}
4.椭圆形
#oval {
width: 200px;
height: 100px;
background: red;
border-radius: 100px / 50px;
}
5.上三角
#triangle-up {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
}
6.下三角
#triangle-down {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid red;
}
7.左三角
#triangle-left {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-right: 100px solid red;
border-bottom: 50px solid transparent;
}
8.右三角
#triangle-right {
width: 0;
height: 0;
border-top: 50px solid transparent;
border-left: 100px solid red;
border-bottom: 50px solid transparent;
}
9.左上角
#triangle-topleft {
width: 0;
height: 0;
border-top: 100px solid red;
border-right: 100px solid transparent;
}
10.右上角
#triangle-topright {
width: 0;
height: 0;
border-top: 100px solid red;
border-left: 100px solid transparent;
}
11.左下角
#triangle-bottomleft {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-right: 100px solid transparent;
}
12.右下角
#triangle-bottomright {
width: 0;
height: 0;
border-bottom: 100px solid red;
border-left: 100px solid transparent;
}
13.箭头
#curvedarrow {
position: relative;
width: 0;
height: 0;
border-top: 9px solid transparent;
border-right: 9px solid red;
transform: rotate(10deg);
}
#curvedarrow:after {
content: "";
position: absolute;
border: 0 solid transparent;
border-top: 3px solid red;
border-radius: 20px 0 0 0;
top: -12px;
left: -9px;
width: 12px;
height: 12px;
transform: rotate(45deg);
}
14.梯形
#trapezoid {
border-bottom: 100px solid red;
border-left: 25px solid transparent;
border-right: 25px solid transparent;
height: 0;
width: 100px;
}
15.平行四边形
#parallelogram {
width: 150px;
height: 100px;
transform: skew(20deg);
background: red;
}
16.星星 (6角)
#star-six {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 100px solid red;
position: relative;
}
#star-six:after {
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 100px solid red;
position: absolute;
content: "";
top: 30px;
left: -50px;
}
17.星星 (5角)
#star-five {
margin: 50px 0;
position: relative;
display: block;
color: red;
width: 0px;
height: 0px;
border-right: 100px solid transparent;
border-bottom: 70px solid red;
border-left: 100px solid transparent;
transform: rotate(35deg);
}
#star-five:before {
border-bottom: 80px solid red;
border-left: 30px solid transparent;
border-right: 30px solid transparent;
position: absolute;
height: 0;
width: 0;
top: -45px;
left: -65px;
display: block;
content: '';
transform: rotate(-35deg);
}
#star-five:after {
position: absolute;
display: block;
color: red;
top: 3px;
left: -105px;
width: 0px;
height: 0px;
border-right: 100px solid transparent;
border-bottom: 70px solid red;
border-left: 100px solid transparent;
transform: rotate(-70deg);
content: '';
}
18.五边形
#pentagon {
position: relative;
width: 54px;
box-sizing: content-box;
border-width: 50px 18px 0;
border-style: solid;
border-color: red transparent;
}
#pentagon:before {
content: "";
position: absolute;
height: 0;
width: 0;
top: -85px;
left: -18px;
border-width: 0 45px 35px;
border-style: solid;
border-color: transparent transparent red;
}
19.六边形
#hexagon {
width: 100px;
height: 55px;
background: red;
position: relative;
}
#hexagon:before {
content: "";
position: absolute;
top: -25px;
left: 0;
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-bottom: 25px solid red;
}
#hexagon:after {
content: "";
position: absolute;
bottom: -25px;
left: 0;
width: 0;
height: 0;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
border-top: 25px solid red;
}
20.八边形
#octagon {
width: 100px;
height: 100px;
background: red;
position: relative;
}
#octagon:before {
content: "";
width: 100px;
height: 0;
position: absolute;
top: 0;
left: 0;
border-bottom: 29px solid red;
border-left: 29px solid #eee;
border-right: 29px solid #eee;
}
#octagon:after {
content: "";
width: 100px;
height: 0;
position: absolute;
bottom: 0;
left: 0;
border-top: 29px solid red;
border-left: 29px solid #eee;
border-right: 29px solid #eee;
}
21.爱心
#heart {
position: relative;
width: 100px;
height: 90px;
}
#heart:before,
#heart:after {
position: absolute;
content: "";
left: 50px;
top: 0;
width: 50px;
height: 80px;
background: red;
border-radius: 50px 50px 0 0;
transform: rotate(-45deg);
transform-origin: 0 100%;
}
#heart:after {
left: 0;
transform: rotate(45deg);
transform-origin: 100% 100%;
}
22.无穷大
#infinity {
position: relative;
width: 212px;
height: 100px;
box-sizing: content-box;
}
#infinity:before,
#infinity:after {
content: "";
box-sizing: content-box;
position: absolute;
top: 0;
left: 0;
width: 60px;
height: 60px;
border: 20px solid red;
border-radius: 50px 50px 0 50px;
transform: rotate(-45deg);
}
#infinity:after {
left: auto;
right: 0;
border-radius: 50px 50px 50px 0;
transform: rotate(45deg);
}
23.菱形
#diamond {
width: 0;
height: 0;
border: 50px solid transparent;
border-bottom-color: red;
position: relative;
top: -50px;
}
#diamond:after {
content: '';
position: absolute;
left: -50px;
top: 50px;
width: 0;
height: 0;
border: 50px solid transparent;
border-top-color: red;
}
24.钻石
#diamond-shield {
width: 0;
height: 0;
border: 50px solid transparent;
border-bottom: 20px solid red;
position: relative;
top: -50px;
}
#diamond-shield:after {
content: '';
position: absolute;
left: -50px;
top: 20px;
width: 0;
height: 0;
border: 50px solid transparent;
border-top: 70px solid red;
}
25.钻戒
#diamond-narrow {
width: 0;
height: 0;
border: 50px solid transparent;
border-bottom: 70px solid red;
position: relative;
top: -50px;
}
#diamond-narrow:after {
content: '';
position: absolute;
left: -50px;
top: 70px;
width: 0;
height: 0;
border: 50px solid transparent;
border-top: 70px solid red;
}
26.钻石2
#cut-diamond {
border-style: solid;
border-color: transparent transparent red transparent;
border-width: 0 25px 25px 25px;
height: 0;
width: 50px;
box-sizing: content-box;
position: relative;
margin: 20px 0 50px 0;
}
#cut-diamond:after {
content: "";
position: absolute;
top: 25px;
left: -25px;
width: 0;
height: 0;
border-style: solid;
border-color: red transparent transparent transparent;
border-width: 70px 50px 0 50px;
}
27.蛋蛋
#egg {
display: block;
width: 126px;
height: 180px;
background-color: red;
border-radius: 50% 50% 50% 50% / 60% 60% 40% 40%;
}
28.吃豆人
#pacman {
width: 0px;
height: 0px;
border-right: 60px solid transparent;
border-top: 60px solid red;
border-left: 60px solid red;
border-bottom: 60px solid red;
border-top-left-radius: 60px;
border-top-right-radius: 60px;
border-bottom-left-radius: 60px;
border-bottom-right-radius: 60px;
}
29.对话泡泡
#talkbubble {
width: 120px;
height: 80px;
background: red;
position: relative;
-moz-border-radius: 10px;
-webkit-border-radius: 10px;
border-radius: 10px;
}
#talkbubble:before {
content: "";
position: absolute;
right: 100%;
top: 26px;
width: 0;
height: 0;
border-top: 13px solid transparent;
border-right: 26px solid red;
border-bottom: 13px solid transparent;
}
30. 12点 爆发
#burst-12 {
background: red;
width: 80px;
height: 80px;
position: relative;
text-align: center;
}
#burst-12:before,
#burst-12:after {
content: "";
position: absolute;
top: 0;
left: 0;
height: 80px;
width: 80px;
background: red;
}
#burst-12:before {
transform: rotate(30deg);
}
#burst-12:after {
transform: rotate(60deg);
}
31. 8点 爆发
#burst-8 {
background: red;
width: 80px;
height: 80px;
position: relative;
text-align: center;
transform: rotate(20deg);
}
#burst-8:before {
content: "";
position: absolute;
top: 0;
left: 0;
height: 80px;
width: 80px;
background: red;
transform: rotate(135deg);
}
32.太极
#yin-yang {
width: 96px;
box-sizing: content-box;
height: 48px;
background: #eee;
border-color: red;
border-style: solid;
border-width: 2px 2px 50px 2px;
border-radius: 100%;
position: relative;
}
#yin-yang:before {
content: "";
position: absolute;
top: 50%;
left: 0;
background: #eee;
border: 18px solid red;
border-radius: 100%;
width: 12px;
height: 12px;
box-sizing: content-box;
}
#yin-yang:after {
content: "";
position: absolute;
top: 50%;
left: 50%;
background: red;
border: 18px solid #eee;
border-radius: 100%;
width: 12px;
height: 12px;
box-sizing: content-box;
}
33.徽章丝带
#badge-ribbon {
position: relative;
background: red;
height: 100px;
width: 100px;
border-radius: 50px;
}
#badge-ribbon:before,
#badge-ribbon:after {
content: '';
position: absolute;
border-bottom: 70px solid red;
border-left: 40px solid transparent;
border-right: 40px solid transparent;
top: 70px;
left: -10px;
transform: rotate(-140deg);
}
#badge-ribbon:after {
left: auto;
right: -10px;
transform: rotate(140deg);
}
34.太空入侵者(电脑游戏名)
#space-invader {
box-shadow: 0 0 0 1em red,
0 1em 0 1em red,
-2.5em 1.5em 0 .5em red,
2.5em 1.5em 0 .5em red,
-3em -3em 0 0 red,
3em -3em 0 0 red,
-2em -2em 0 0 red,
2em -2em 0 0 red,
-3em -1em 0 0 red,
-2em -1em 0 0 red,
2em -1em 0 0 red,
3em -1em 0 0 red,
-4em 0 0 0 red,
-3em 0 0 0 red,
3em 0 0 0 red,
4em 0 0 0 red,
-5em 1em 0 0 red,
-4em 1em 0 0 red,
4em 1em 0 0 red,
5em 1em 0 0 red,
-5em 2em 0 0 red,
5em 2em 0 0 red,
-5em 3em 0 0 red,
-3em 3em 0 0 red,
3em 3em 0 0 red,
5em 3em 0 0 red,
-2em 4em 0 0 red,
-1em 4em 0 0 red,
1em 4em 0 0 red,
2em 4em 0 0 red;
background: red;
width: 1em;
height: 1em;
overflow: hidden;
margin: 50px 0 70px 65px;
}
35.电视
#tv {
position: relative;
width: 200px;
height: 150px;
margin: 20px 0;
background: red;
border-radius: 50% / 10%;
color: white;
text-align: center;
text-indent: .1em;
}
#tv:before {
content: '';
position: absolute;
top: 10%;
bottom: 10%;
right: -5%;
left: -5%;
background: inherit;
border-radius: 5% / 50%;
}
36.雪佛龙
#chevron {
position: relative;
text-align: center;
padding: 12px;
margin-bottom: 6px;
height: 60px;
width: 200px;
}
#chevron:before {
content: '';
position: absolute;
top: 0;
left: 0;
height: 100%;
width: 51%;
background: red;
transform: skew(0deg, 6deg);
}
#chevron:after {
content: '';
position: absolute;
top: 0;
right: 0;
height: 100%;
width: 50%;
background: red;
transform: skew(0deg, -6deg);
}
37.放大镜
#magnifying-glass {
font-size: 10em;
display: inline-block;
width: 0.4em;
box-sizing: content-box;
height: 0.4em;
border: 0.1em solid red;
position: relative;
border-radius: 0.35em;
}
#magnifying-glass:before {
content: "";
display: inline-block;
position: absolute;
right: -0.25em;
bottom: -0.1em;
border-width: 0;
background: red;
width: 0.35em;
height: 0.08em;
transform: rotate(45deg);
}
38.Facebook图标
#facebook-icon {
background: red;
text-indent: -999em;
width: 100px;
height: 110px;
box-sizing: content-box;
border-radius: 5px;
position: relative;
overflow: hidden;
border: 15px solid red;
border-bottom: 0;
}
#facebook-icon:before {
content: "/20";
position: absolute;
background: red;
width: 40px;
height: 90px;
bottom: -30px;
right: -37px;
border: 20px solid #eee;
border-radius: 25px;
box-sizing: content-box;
}
#facebook-icon:after {
content: "/20";
position: absolute;
width: 55px;
top: 50px;
height: 20px;
background: #eee;
right: 5px;
box-sizing: content-box;
}
39.月亮
#moon {
width: 80px;
height: 80px;
border-radius: 50%;
box-shadow: 15px 15px 0 0 red;
}
40.旗
#flag {
width: 110px;
height: 56px;
box-sizing: content-box;
padding-top: 15px;
position: relative;
background: red;
color: white;
font-size: 11px;
letter-spacing: 0.2em;
text-align: center;
text-transform: uppercase;
}
#flag:after {
content: "";
position: absolute;
left: 0;
bottom: 0;
width: 0;
height: 0;
border-bottom: 13px solid #eee;
border-left: 55px solid transparent;
border-right: 55px solid transparent;
}
41.圆锥
#cone {
width: 0;
height: 0;
border-left: 70px solid transparent;
border-right: 70px solid transparent;
border-top: 100px solid red;
border-radius: 50%;
}
42.十字架
#cross {
background: red;
height: 100px;
position: relative;
width: 20px;
}
#cross:after {
background: red;
content: "";
height: 20px;
left: -40px;
position: absolute;
top: 40px;
width: 100px;
}
43.根基
#base {
background: red;
display: inline-block;
height: 55px;
margin-left: 20px;
margin-top: 55px;
position: relative;
width: 100px;
}
#base:before {
border-bottom: 35px solid red;
border-left: 50px solid transparent;
border-right: 50px solid transparent;
content: "";
height: 0;
left: 0;
position: absolute;
top: -35px;
width: 0;
}
44.指示器
#pointer {
width: 200px;
height: 40px;
position: relative;
background: red;
}
#pointer:after {
content: "";
position: absolute;
left: 0;
bottom: 0;
width: 0;
height: 0;
border-left: 20px solid white;
border-top: 20px solid transparent;
border-bottom: 20px solid transparent;
}
#pointer:before {
content: "";
position: absolute;
right: -20px;
bottom: 0;
width: 0;
height: 0;
border-left: 20px solid red;
border-top: 20px solid transparent;
border-bottom: 20px solid transparent;
}
45.锁
#lock {
font-size: 8px;
position: relative;
width: 18em;
height: 13em;
border-radius: 2em;
top: 10em;
box-sizing: border-box;
border: 3.5em solid red;
border-right-width: 7.5em;
border-left-width: 7.5em;
margin: 0 0 6rem 0;
}
#lock:before {
content: "";
box-sizing: border-box;
position: absolute;
border: 2.5em solid red;
width: 14em;
height: 12em;
left: 50%;
margin-left: -7em;
top: -12em;
border-top-left-radius: 7em;
border-top-right-radius: 7em;
}
#lock:after {
content: "";
box-sizing: border-box;
position: absolute;
border: 1em solid red;
width: 5em;
height: 8em;
border-radius: 2.5em;
left: 50%;
top: -1em;
margin-left: -2.5em;
}
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