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HTML

              
                <h1>
  Mask border for one side of an element
</h1>
<p>
  This demo uses the <strong>mask</strong> CSS property. You can use multiple values, so to get this effect we are chaining together our border (in this case, a caret icon) and a simple rectangle shape to take up the remainder of the element.
</p>
<div class="image-container">
  <!-- Image with a border on the left-hand side -->
  <div class="image border-left">
    <img src="https://images.unsplash.com/photo-1597163538726-ecc20df70005?ixlib=rb-1.2.1&q=85&fm=jpg&crop=entropy&cs=srgb&izxid=eyJhcHBfaWQiOjE0NTg5fQ"/>
  </div>

  <!-- Image with a border on the right-hand side -->
  <div class="image border-right">
    <img src="https://images.unsplash.com/photo-1597163538726-ecc20df70005?ixlib=rb-1.2.1&q=85&fm=jpg&crop=entropy&cs=srgb&ixid=eyJhcHBfaWQiOjE0NTg5fQ"/>
  </div>

  <!-- Image with a top border -->
  <div class="image border-top">
    <img src="https://images.unsplash.com/photo-1597163538726-ecc20df70005?ixlib=rb-1.2.1&q=85&fm=jpg&crop=entropy&cs=srgb&ixid=eyJhcHBfaWQiOjE0NTg5fQ"/>
  </div>

  <!-- Image with a bottom border -->
  <div class="image border-bottom">
    <img src="https://images.unsplash.com/photo-1597163538726-ecc20df70005?ixlib=rb-1.2.1&q=85&fm=jpg&crop=entropy&cs=srgb&ixid=eyJhcHBfaWQiOjE0NTg5fQ"/>
  </div>
</div>
              
            
!

CSS

              
                /* Unrelated styles */
html {
  font-family: Inconsolata, sans-serif;
  text-align: center;
  background: #FFF8E1;
}

h1 {
  font-size: 21px;
}

p {
  font-size: 16px;
  line-height: 1.65;
  max-width: 550px;
  margin: 0 auto;
  margin-bottom: 10px
}

.image-container { 
  display: flex;
  max-width: 750px;
  margin: 0 auto;
}

.image {
  flex: 0 0 22%;
  margin-right: 3%;
}

.image img {
  width: 100%;
}

/* end unrelated styles */



/* 
The border: 
 - Using the mask CSS property, start the pattern on one side of the element. This can be top, right, bottom or left. 
 - Make the image a fixed width and height (these can be a percentage).
 - Repeat vertically or horizontally, depending on what side you want your border on. This can be `repeat-y` or `repeat-x`.

The remainder:
 - For our rectangle value, which will take up the remainder of the space, place this on the *opposite* side of whatever you chose for your border image.
 - If this is a top/bottom border, set the width/height to `calc(100% - [size-of-your-border]) auto`. 
 - If this is a left/right border, set the width/height to `auto calc(100% - [size-of-your-border])`. You may need to fiddle with the pixel value to make sure there's no gap on resize (in my example, you may note that I needed to set this to 10px rather than 16px)
 - This should repeat the same direction as your border, either `repeat-x` or `repeat-y`.


That's it!

*/

.border-left {
  -webkit-mask: url(https://assets.codepen.io/339955/caret-left.svg) left / 16px 16px repeat-y, 
                url(https://assets.codepen.io/339955/rect.svg) right / calc(100% - 10px) auto repeat-y;
  mask: url(https://assets.codepen.io/339955/caret-left.svg) left / 16px 16px repeat-y,
        url(https://assets.codepen.io/339955/rect.svg) right / calc(100% - 10px) auto repeat-y;
}

.border-right {
  -webkit-mask: url(https://assets.codepen.io/339955/caret-right.svg) right / 16px 16px repeat-y, 
                url(https://assets.codepen.io/339955/rect.svg) left / calc(100% - 10px) repeat-y;
  mask: url(https://assets.codepen.io/339955/caret-right.svg) right / 16px 16px repeat-y,
        url(https://assets.codepen.io/339955/rect.svg) left / calc(100% - 10px) repeat-y;
}


.border-top {
  -webkit-mask: url(https://assets.codepen.io/339955/caret-up.svg) top / 16px 16px repeat-x, 
                url(https://assets.codepen.io/339955/rect.svg) bottom / auto calc(100% - 10px) repeat-x;
  mask: url(https://assets.codepen.io/339955/caret-up.svg) top / 16px 16px repeat-x, 
        url(https://assets.codepen.io/339955/rect.svg) bottom / auto calc(100% - 10px) repeat-x;
}


.border-bottom {
  -webkit-mask: url(https://assets.codepen.io/339955/caret-down.svg) bottom / 16px 16px repeat-x, 
                url(https://assets.codepen.io/339955/rect.svg) top / auto calc(100% - 10px) repeat-x;
  mask: url(https://assets.codepen.io/339955/caret-down.svg) bottom / 16px 16px repeat-x, 
        url(https://assets.codepen.io/339955/rect.svg) top / auto calc(100% - 10px) repeat-x;
}
              
            
!

JS

              
                
              
            
!
999px

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