How to use clip-path property for border in css

Question

I have clip-part to make "cut corner" effect.

I would like to change background to white and use green border. Problem is, when I change ba

Answer 1

add some gradient to fill the missing spaces:

.test {
  background: red;
  width: 100px;
  height: 100px;
  box-sizing:border-box;
  
  /* CORNERS */
    clip-path: polygon(10px 0%, calc(100% - 10px) 0%, 100% 10px, 100% calc(100% - 10px), calc(100% - 10px) 100%, 10px 100%, 0% calc(100% - 10px), 0% 10px);
}

.test:hover {
  --grad:transparent 49.5%,green 50%;
  background: 
    linear-gradient(to top right   ,var(--grad)) top    right,
    linear-gradient(to top left    ,var(--grad)) top    left,
    linear-gradient(to bottom right,var(--grad)) bottom right,
    linear-gradient(to bottom left ,var(--grad)) bottom left,
    white;
  background-size:13px 13px; /* 10px of the clip-path + 3px of border */
  background-repeat:no-repeat;
  background-origin:border-box;
  cursor: pointer;
  
  border: 3px solid green;
}

<div class='test'>
 </div>

Answer 2

i'll make an answer of my comment for readability :

For infos , if clip-path is used on a 2 level container, it is possible to add a shadow around the translucide edges with drop-shadow() filter .

• clip-path applied on the child
• drop-shadow() on the parent
• without a blur , it looks like a border no matter the shape : https://jsfiddle.net/q9tdpvfg/

jsfiddle demo in the snippet below:

.test div {
  background: red;
  width: 100px;
  height: 100px;
  /* CORNERS */
  clip-path: polygon(10px 0%, calc(100% - 10px) 0%, 100% 10px, 100% calc(100% - 10px), calc(100% - 10px) 100%, 10px 100%, 0% calc(100% - 10px), 0% 10px);
}

.test:hover {
  filter: drop-shadow(0px 3px 0px green) drop-shadow(3px 0px 0px green) drop-shadow(-3px 0px 0px green) drop-shadow(0px -3px 0px green);
  /* made 1 for each sides */
}

.test:hover div {
  background: white;
  cursor: pointer;
}

.test {
  width: max-content;
}

.test div {
  /* demo purpose */
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
}

<div class='test'>
  <div>
    TEST
  </div>
</div>

Answer 3

As far as I know, it's not really possible to make a border around an element with a clip-path. This method uses inside and outside elements. Source: https://codepen.io/bennettfeely/pen/azJWWX/

.outside {
  position: relative;
    width: 70vmin;
    height: 70vmin;
    background: red;
    -webkit-clip-path: polygon(50% 0%, 83% 12%, 100% 43%, 94% 78%, 68% 100%, 32% 100%, 6% 78%, 0% 43%, 17% 12%);
clip-path: polygon(50% 0%, 83% 12%, 100% 43%, 94% 78%, 68% 100%, 32% 100%, 6% 78%, 0% 43%, 17% 12%);
}

.inside {
  position: absolute;
  top: 5px;
  left: 5px;
  right: 5px;
  bottom: 5px;
  background: red;
  -webkit-clip-path: polygon(50% 0%, 83% 12%, 100% 43%, 94% 78%, 68% 100%, 32% 100%, 6% 78%, 0% 43%, 17% 12%);
  clip-path: polygon(50% 0%, 83% 12%, 100% 43%, 94% 78%, 68% 100%, 32% 100%, 6% 78%, 0% 43%, 17% 12%);
}

.inside:hover {
  background: white;
  transition: all .2s;
}

.outside:hover {
  background: green;
  transition: all .2s;
}

/* Center the demo */
html, body { height: 100%; }
body {
    display: flex;
    justify-content: center;
    align-items: center;
  background: papayawhip;
}

<div class="outside">
  <div class="inside"></div>
</div>