Here is my HTML:
<header>
<div class="set">
<div class="set">
<div class="set">
<div class="set">
<div class="set">
<span>123</span>
</header>
How do I effectively use CSS Flex to make all the header > div elements effectively float: left; while making the header > span element effectively float: right; while keeping it on the same main axis?