Say you want to position something within its container, then the element you are trying to position needs to have:
position: absolute;
But the parent container can simply have:
position: relative;
So in full:
<div class="container">
<div class="abs-position">
Hello world!
</div>
</div>
And then simple CSS:
.container {
position: relative;
}
.abs-position {
position: absolute;
left: 100px;
height: 200px;
}
Easy solution to an age old problem.