JSFiddle - React, Tailwind, and code Playground

HTML

<div class="z1">
            
<div class="z1l">
<br/><br/><br/><br/><br/><br/><br/><br/><br/><br/>
</div>
            
<div class="z1r">
<br/><br/><br/><br/><br/><br/><br/><br/><br/><br/>
</div>
            
</div>

CSS

body,
html {
  font-family: 'Open Sans', Arial, sans-serif;
  height: 100%;
  background: #12121A;
}

.z1 {
  padding: 0px 50px 0px 50px;
  margin: 80px auto 80px;
  max-width: 1200px;
  min-width: 280px;
  font-size: 14px;
  color: #fff;
  font-weight: 400;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
}
.z1l, .z1r {
  -ms-flex-negative: 0;
  flex-shrink: 0;
  position: relative;
}
.z1l {
  width:68%;
  background: #999;
}
.z1r {
  width:32%;
  background: #ccc;
}

@media only screen and (max-width:900px) {
  .z1 {
    -ms-flex-wrap: wrap;
    flex-wrap: wrap;
  }
  .z1l {
    width: 100%;
  }
  .z1r {
    width: 100%;
  }
  }