<div class="block-level-element one">Block Level Element</div>
<div class="block-level-element two">Block Level Element</div>
.block-level-element {
  text-align:center;
  padding:4em 0;
  border:1px solid black;
  color:white;
}
.one {
  background:green;
}

.two {
  background:blue;
}

@media only screen and (min-width: 40em) {
  .block-level-element {
    float:left;
    margin:0 1%;
    width:47%;
  }
}
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