Flex responsive

http://www.w3schools.com/cssref/tryit.asp?filename=trycss3_flex

by Roberto Apasajja

HTML

<div id="row99">
  <div class="one">RED</div>
  <div class="two">BLUE</div>  
  <div class="three">Green div with more content.</div>
</div>

<p><b>Note:</b> Internet Explorer 9 and earlier versions do not support the flex property.</p>

<p><b>Note:</b> Internet Explorer 10 supports an alternative, the -ms-flex property. IE11 and newer versions fully support the flex property (do not need the -ms- prefix).</p>

<p><b>Note:</b> Safari 6.1 (and newer) supports an alternative, the -webkit-flex property.</p>

CSS

#row99 {
    width: 100%;
    height: 90px;
    display: -webkit-flex; /* Safari */
    display: flex;
}

.one {
  background: coral;
  -webkit-flex: 1;  /* Safari 6.1+ */
  -ms-flex: 1;  /* IE 10 */    
  flex: 1;
}

.two {
  background: lightblue;
  -webkit-flex: 2;  /* Safari 6.1+ */
  -ms-flex: 2;  /* IE 10 */    
  flex: 2;
}

.three {
  background: lightgreen;
  -webkit-flex: 1;  /* Safari 6.1+ */
  -ms-flex: 1;  /* IE 10 */    
  flex: 1;
}

@media screen and (max-width: 600px) {
  #row99 {
    display: inline;
  }
}