How do I add a border to an (8 point star) css sha

问题:

How do I add a red border outside this 8 point star? Or is there a simple svg solution anyone knows of?

IS: NEED:

JS fiddle

HTML

<div id="star8"></div>

CSS

#star8 {
 border: 3px solid red;
 background: blue; width: 80px;
 height: 80px;
 position: relative;
 -webkit-transform: rotate(20deg);
 -moz-transform: rotate(20deg);
 -ms-transform: rotate(20deg);
 -o-transform: rotate(20eg);
 }
#star8:before {
 content: "";
 position: absolute;
 top: 0;
 left: 0;
 height: 80px;
 width: 80px;
 background: blue;
 -webkit-transform: rotate(135deg);
 -moz-transform: rotate(135deg);
 -ms-transform: rotate(135deg);
 -o-transform: rotate(135deg);
 }

回答1:

you may use mix-blend-mode and eventually the other pseudo : DEMO

#star8:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  transform: rotate(135deg);
  box-shadow: 0 0 0 3px red;::* a border works too */
  mix-blend-mode:overlay;
}

#star8 {
  margin: 2em;
  border: 3px solid red;
  background: blue;
  width: 80px;
  height: 80px;
  position: relative;
  transform: rotate(20deg);
}

#star8:before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  background: blue;
  transform: rotate(135deg);
}

#star8:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  transform: rotate(135deg);
  box-shadow: 0 0 0 3px red;
  mix-blend-mode:overlay;
}

<div id="star8"></div>

---

without mix-blend-mode but z-index and :after

#star8 {
  margin: 2em;
  border: 3px solid red;
  background: blue;
  width: 80px;
  height: 80px;
  position: relative;
  transform: rotate(20deg);
}

#star8:before {
  content: "";
  position: absolute;
  z-index:-1;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  background: blue;
  transform: rotate(135deg);
  box-shadow: 0 0 0 3px red;
}

#star8:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  background: blue;
  transform: rotate(0deg);
}

<div id="star8"></div>

You can also draw only parts of bg (via linear-gradient) to hide the border parts unwanted and add some text inside : http://codepen.io/gc-nomade/pen/KWNmqw

回答2:

SVG solution

This can be created with a single svg path. Adding outline can be done with adding a stroke property to the path

<svg viewBox="-1 -1 50 50" width="200px">
  <path d="M 35,40 30,48 21,42 11,44 9,34 0,30 6,20 4,10 14,8 20,0 28,5 38,3 l 1,10 8,5 -5,8 2,10z" stroke="red" stroke-linejoin="bevel" fill="black" />
</svg>

回答3:

The reason the div looks the way it does currently is that you don't actually have an 8 pointed star, you have 2 squares superimposed on one another.

The first step is to add the outline to the :before pseudo class. The second is to add an :after pseudo class with no outline, rotated to the same position as the original div, to cover the outline drawn by :before overlapping the original div.

Demo: https://jsfiddle.net/hj1eh6md/

and CSS:

#star8 {
 border: 3px solid red;
 background: olive; 
 width: 80px;
 height: 80px;
 position: relative;
 -webkit-transform: rotate(20deg);
 -moz-transform: rotate(20deg);
 -ms-transform: rotate(20deg);
 -o-transform: rotate(20eg);
}
#star8:before {
 border: 3px solid red;
 content: "";
 position: absolute;
 top: 0;
 left: 0;
 height: 80px;
 width: 80px;
 background: olive;
 -webkit-transform: rotate(135deg);
 -moz-transform: rotate(135deg);
 -ms-transform: rotate(135deg);
 -o-transform: rotate(135deg);
}
#star8:after{
 content: "";
 position: absolute;
 top: 0;
 left: 0;
 height: 80px;
 width: 80px;
 background: olive;
}

回答4:

Just overlay another rect over it in :after, covering up the red border. http://codepen.io/anon/pen/qbrQZa

#star8:after {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  height: 80px;
  width: 80px;
  background: blue;
}

You should also make #star8:before only 77x77 in size to make it fit.