CSS

CSS (Cascading-Style-Sheets) is a language for defining how a document, typically written in HTML is presented.

Common usages

Position two elements on top of eachother

Using position: absolute:

<section class="container">
	<div class="child">B1</div>
	<div class="child">B2</div>
</section>

/* With this method, the child will always be positioned absolutely. */
/* This might be what you want, but likely you'll want it to stick */
/* to the container. */
.child {
	position: absolute;
}

Using position:absolute with a relative parent

.container {
	position: relative;
}

.child {
	position: absolute;

	/* Position up the top left of the container at all times. */
	top: 0;
	left: 0;
}