background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 12'%3E%3Cpath d='m12 0l12 12h-24z' fill='%23fff'/%3E%3C/svg%3E");
position: relative on the element establishes a Cartesian positioning context for pseudo elements.
::after defines a pseudo element.
background-image: url(...) adds the SVG shape (a 24x12 triangle) as the background image of the pseudo element, which repeats by default. It must be the same color as the block that is being separated. For other shapes, we can use the URL-encoder for SVG.
position: absolute takes the pseudo element out of the flow of the document and positions it in relation to the parent.
width: 100% ensures the element stretches the entire width of its parent.
height: 12px is the same height as the shape.
bottom: 0 positions the pseudo element at the bottom of the parent.