Absolute positioning with no positioned ancestor

This is an unpositioned or just normal flow div container. Its green child might be way down to the right quite outside this yellow box or walking annoyingly all over it depending on how wide and high you have your browser. If you don't want this, then 'position' the parent

CSS HTML
.one {
color: #000;
background: #cfc; 
width: 800px;  
height: 10em;
padding: .5em;
}

.two {
position: absolute;
left: 50%;
bottom: 0;
color: #000;
background: #fcc;
padding: .5em;
}
<div class="one">This is an unpositioned or just
normal flow yellow div container ...
<div class="two"> This is an absolutely positioned green
descendant of the yellow div container...
</div>
</div>
This is an absolutely positioned descendant of the div container in the HTML. But it gets to be positioned in relation to the viewport, not its parent div which is not 'positioned'.