Applying a transform => new stacking context
Applying a transform on an element (unless its value is none) creates a new stacking context and the element is going to act as a containing block for any position: fixed; children it may have.
by thebabydino
HTML
<div class='parent'>
<div class='child'>No transform applied on my parent.</div>
</div>
<div class='parent'>
<div class='child'><code>transform: rotate(30deg)</code> applied on my parent.</div>
</div>
CSS
.child {
background: darkslateblue;
color: lemonchiffon;
}