<!DOCTYPE html>
<style>
#flexbox {
  width: 500px;
  display: flex;
  direction: rtl;
}

#redbox {
  background: red;
  flex: 1;
}

#greenbox {
  background: green;
  flex: 1;
}

</style>
<p>There should be a green box followed by a red box, both on the same line.
<div id="flexbox">
  <div id="redbox">A</div>
  <div id="greenbox">B</div>
</div>