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HTML

              
                <ul class="boxes">
  
  <li class="box  box-alpha">
     <header class="box-header">Cross-browser : the circle works from Opera 15, Chrome 23, Firefox 17.</header>
     <footer class="box-footer">Firefox between 4 and 17 does clip the circle, but does not vertically center it…</footer>
  </li>
  
  <li class="box  box-beta">
     <header class="box-header">The square fallback works from Opera 10.6, Chrome 14, IE9 — IE8 not centered, Safari 1.</header>
     <footer class="box-footer"></footer>
  </li>
  
  <li class="box  box-gamma">
     <header class="box-header"></header>
     <footer class="box-footer">IE7 gracefully degrades with no generated content.</footer>
  </li>
  
  <li class="box  box-delta">
     <header class="box-header"></header>
     <footer class="box-footer">Check if Firefox could clip without SVG.</footer>
  </li>
  
</ul>

<div class="text">
  <h2>What you should know</h2>
  <ol>
    <li><strong>Chrome’s good. That’s it.</strong> Safari 6.1 should be good too.</li>
    <li>Firefox’ not bad — but read this :
      <ul>
        <li>FF can’t clip a basic shape like <<code>>clip-path: circle( 50%, 50%, 5em );</code>.<b>That’s bad.</b></li>
        <li>But it can clip any <abbr title="HyperText Markup Language">HTML</abbr> element when referencing a <abbr title="Scalable Vector Graphics">SVG</abbr> <code>clipPath</code> element (watch my <abbr title="Document Object Model">DOM</abbr>). That’s pretty good.</li>
        <li>Bad thing is : you have to specify dimensions. Percentage won’t work and you shall cry. Relative units like <code>em</code> will work, but behind FF 17, it becomes weird. <b>That’s a bad thing because you won’t be able to use it on a fluid layout.</b></li>
        <li>Prior to version 4, FF will fallback to the ol’ good <abbr title="Cascadinc StyleSheet">CSS</abbr> 2.1 <code>clip</code> property. Which is good, but is restricted to rectangle shapes (as you may know).</li>
      </ul>
    </li>
    <li><b>Opera 15 and up is just good.</b></li>
    <li>Opera from 10.6 to 15 fallback to <abbr title="Cascadinc StyleSheet">CSS</abbr> 2.1 <code>clip</code> property. <b>Pretty good.</b></li>
    <li><b>Let’s talk about IE.</b> Please sit up. 
      <ul>
        <li>That just doesn’t work on IE 11 and lower. Surprised ? You should be ! IE9 to 11 can clip when referencing a <code>clipPath</code> element (just like Firefox, remember ?) but it can only clip inside a <abbr title="Scalable Vector Graphics">SVG</abbr> element. That means you could use <code>ForeignObject</code> to wrap your <abbr title="HyperText Markup Language">HTML</abbr> inside any <abbr title="Scalable Vector Graphics">SVG</abbr> and it should work ! More test to come…</li>
         <li>IE8 will always fallback to <abbr title="Cascadinc StyleSheet">CSS</abbr> 2.1 <code>clip</code> property, but it’s very good ! In our test case, that means it only misses the circle thing — but that’s obvious and logical since it can’t draw a border-radius anyway. <b>Squares everywhere, yay !</b></li>
         <li>IE7 just doesn’t do anything with pseudo-elements so it just do a good job.</li>
      </ul>
    </li>
  </ol>
  <h2>What you could do</h2>
  <p>It’s pretty good when you can specify width and height.</p>
  <p>But it maybe doable with other ressources :</p>
  <ul>
    <li><a href="http://www.w3.org/TR/css-masking-1/#masking"><code>mask-image</code></a> : since it’s now part of the specs, you may try. You can position it just like a background, and the Apple’s version is from 2008.</li>
    <li>Pure SVG. Yeah, I know.</li>
    <li>Javascript may help for each of these tricks…</li>
  </ul>
</div>

<svg width="800" height="390">
  <defs>
    <clipPath id="circle">
      <circle cx="50%" cy="50%" r="80" />
    </clipPath>    
  </defs>
</svg>
              
            
!

CSS

              
                *, 
:after,
:before {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}

/* IE8 Express */
section,
header,
footer { display: block; }

/* Références :
 * https://codepen.io/iamvdo/pen/EIjLa
 * https://codepen.io/iamvdo/pen/hasAm
 * http://www.24joursdeweb.fr/2013/les-masques-css/
 * https://www.html5rocks.com/en/tutorials/masking/adobe/
 * http://docs.webplatform.org/wiki/css/properties/clip-path
 * https://developer.mozilla.org/en-US/docs/Web/SVG/Tutorial/Clipping_and_masking
 * http://www.w3.org/TR/SVG/masking.html#ClippingPaths
 * http://www.w3.org/TR/css-masking-1/#masking
 * https://www.webkit.org/blog/181/css-masks/
 * https://developer.apple.com/library/safari/documentation/AppleApplications/Reference/SafariCSSRef/Articles/StandardCSSProperties.html#//apple_ref/doc/uid/TP30001266-VisualEffects
 * http://thenittygritty.co/css-masking
*/

/**
 * 1. Position is everything — and very useful to place the ::before pseudo-element :)
 * 2. Giving background. 
 * 3. Used to position SVG shape used as a fallback for clip-path: <basic-shape>.
 * 4. Useful for IE8.
 */
.boxes {
  list-style: none;
  padding: 0;
  margin: 2em auto 0;
  overflow: hidden;
  position: relative; /* 1 */
  background-image : url(http://placehold.it/800x400); /* 2 */
  max-width: 800px; /* 3 */
  z-index: 1; /* 4 */
}

/**
 * @note : The trick is to create a pseudo-element with the exact same dimensions and background than the .boxes, and stack it above. Then we’ll clip it in order to make it a simple circle, creating a « see-hrough » like effect.
 * 1.  Creating ::before with the same dimensions as its relative parent (.boxes) 
 * 2. Giving the same background. 
 * 3. Using a simple rectangle clip for simplest browsers (a.k.a. IE). 
 * 4. Clipping the pseudo-element to create the centered circle. 
 * 5. SVG shape is more cross-browser. Circle is centered with <cx> and <cy> attributes : 400 = 800(.boxes’width)/2 and 12em = 6em(.box’s height + margin-bottom)*2.
 */
.boxes:before {
  content: '';
  position: absolute; /* 1 */
  z-index: 2; /* 1 */
  bottom: 0; /* 1 */
  right: 0; /* 1 */
  left: 0; /* 1 */
  top: 0; /* 1 */   
  background-image: inherit; /* 2 */  
  clip: rect( 7em, 30em, 17em, 20em ); /* 3 */
  -webkit-clip-path: circle( 50%, 50%, 5em ); /* 4 */
  clip-path: url(#circle); /* 5 */
  clip-path: circle( 50%, 50%, 5em );
}
/*
/**
 * 1. Width and height are equal t get a square and 5em for proportions with other elements;
 * 2. Making a circle;
 * 3. Centering the circle.
 */
.boxes:after {
  content: '';
  position: absolute;
  background: #34495e;
  height: 5em; /* 1 */
  width: 5em; /* 1 */
  border: .5em solid #2f3e51;
  border-radius: 50%; /* 2 */
  z-index: 3;
  left: 44%; /* 3 */
  top: 40%; /* 3 */  
  left: calc( 50% - 2.5em ); /* 3 */
  top: calc( 50% - 2.5em ); /* 3 */    
}

/**
 * 1. Feel free to move to inline-block or whatever
 * 2. Useful for IE8.
 */
.box {
  color: #fff;
  float: left; /* 1 */  
  margin: 1em;
  position: relative; /* 2 */
  z-index: -1; /* 2 */
  width: 45%; /* 2 */
  width: calc( 50% - 2em );
}

.box-header,
.box-footer { 
  min-height: 5em; 
  padding: 1em;
}

.box-alpha .box-header { background: #1abc9c; }

.box-alpha .box-footer { background: #148f77; }

.box-beta .box-header { background: #2ecc71; }

.box-beta .box-footer { background: #25a25a; }

.box-gamma .box-header { background: #217dbb; }

.box-gamma .box-footer { background: #3498db; }

.box-delta .box-header { background: #804399; }

.box-delta .box-footer { background: #9b59b6; }

/* Mobile helper */
@media (max-width: 800px) {
  .boxes:after,
  .boxes:before { content: none; }
  
  .box {
    float: none;
    margin: 2%;
    width: 96%;    
  }
}

/* Legend */
.text {
  margin: 2em auto;
  max-width: 800px;
}
              
            
!

JS

              
                
              
            
!
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