边界CSS内的边框

Question

在CSS Triangle教程的帮助下,我学会了创建三角形形状.

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

我正在尝试为三角形添加边框,但我无法做到.

我取得的成就:

预期:(尝试类似灰色边框)

检查一下 JSFiddle

坚持没有从哪里开始这个.我试过了outline,但都没有用(我知道它不起作用).

感谢您花时间阅读我的问题.

任何帮助表示赞赏.

注意:我在CSS中尝试这个而不是使用图像.

Answer 1

当使用CSS边框创建主三角形或箭头时,如果不使用额外的元素,则无法为其添加另一个边框.以下是几个选项.

选项1:使用更大尺寸的伪元素并将其定位在父元素后面以产生边界效果.

.arrow-down {
  position: relative;
  width: 0;
  height: 0;
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  border-top: 20px solid #ccc;
}
.arrow-down:before {
  position: absolute;
  content: "";
  left: -22px;
  top: -20px;
  height: 0px;
  width: 0px;
  border-left: 21px solid transparent;
  border-right: 21px solid transparent;
  border-bottom: 21px solid transparent;
  border-top: 21px solid black;
  z-index: -1;
}

<div class="arrow-down"></div>

.arrow-down:before {
  position: absolute;
  content: "";
  left: -22px;
  top: -20px;
  height: 0px;
  width: 0px;
  border-left: 21px solid transparent;
  border-right: 21px solid transparent;
  border-bottom: 21px solid transparent;
  border-top: 21px solid black;
  z-index: -1;
}

选项2:旋转元素(具有边框hack以生成三角形)然后添加一个元素box-shadow.

.arrow-down {
  width: 0;
  height: 0;
  margin: 10px;
  border-left: 0px solid transparent;
  border-right: 30px solid transparent;
  border-top: 30px solid #ccc;
  -ms-transform: rotate(225deg);  /* IE 9 */
  -webkit-transform: rotate(225deg);  /* Chrome, Safari, Opera */
  -moz-transform: rotate(225deg);
  transform: rotate(225deg);
  box-shadow: 0px -3px 0px -1px #444;
}

<div class="arrow-down"></div>

.arrow-down {
  width: 0;
  height: 0;
  margin: 10px;
  border-left: 0px solid transparent;
  border-right: 30px solid transparent;
  border-top: 30px solid #ccc;
  transform: rotate(225deg); /* browser prefixes added in snippet */
  box-shadow: 0px -3px 0px -1px #444;
}

在Chrome v24和Safari v5.1.7中测试过.应该在其他CSS3兼容的浏览器中工作.

以下选项不直接回答问题,因为它不在边框内执行边框,而是以其他方式生成带边框的箭头/三角形.

选项3:在元素上使用线性渐变,旋转它以生成三角形,然后使用普通边框属性为其添加边框.

.arrow-down {
  width: 30px;
  height: 30px;
  margin: 10px;
  border-left: 2px solid #444;
  background: -webkit-linear-gradient(45deg, #ccc 50%, transparent 50%);
  background: -moz-linear-gradient(45deg, #ccc 50%, transparent 50%);
  background: -o-linear-gradient(45deg, #ccc 50%, transparent 50%);
  background: linear-gradient(45deg, #ccc 50%, transparent 50%);
  -webkit-transform: rotate(-45deg);
  -moz-transform: rotate(-45deg);
  transform: rotate(-45deg);
  -webkit-backface-visibility:hidden; /** <-- to prevent diagonal line aliasing in chrome **/
}

<div class="arrow-down"></div>

.arrow-down {
  width: 30px;
  height: 30px;
  margin: 10px;
  border-left: 2px solid #444;
  background: linear-gradient(45deg, #ccc 50%, transparent 50%);
  transform: rotate(-45deg);
  backface-visibility:hidden;
}

选项4:使用旋转的伪元素(背景为三角形的颜色)生成三角形,然后为其添加法线边框.父元素的溢出设置为隐藏,并且伪元素被适当地定位,以便仅显示其一半(创建三角形的错觉).

.arrow-down {
  position: relative;
  height: 50px;
  width: 50px;
  overflow: hidden;
}
.arrow-down:before {
  position: absolute;
  content: '';
  top: -webkit-calc(100% * -1.414 / 2);
  top: calc(100% * -1.414 / 2);
  left: 0px;
  height: 100%;
  width: 100%;
  background: #CCC;
  border-left: 2px solid #444;
  -webkit-transform: rotate(-45deg);
  -moz-transform: rotate(-45deg);
  transform: rotate(-45deg);
}

<div class="arrow-down"></div>

.arrow-down:before {
  position: absolute;
  content: '';
  top: calc(100% * -1.414 / 2);
  left: 0px;
  height: 100%;
  width: 100%;
  background: #CCC;
  border-left: 2px solid #444;
  transform: rotate(-45deg);
}