Top and bottom margins of blocks are sometimes combined (collapsed) into a single margin whose size is the largest of the margins combined into it, a behavior known as margin collapsing.

CSS CSS Box Model Reference

CSS Box Model is a CSS module that defines the rectangular boxes, including their padding and margin, that are generated for elements and laid out according to the visual formatting model.

CSS CSS Box Model CSS Reference Overview

In a document, each element is represented as a rectangular box. Determining the size, properties — like its color, background, borders aspect — and the position of these boxes is the goal of the rendering engine.

Beginner CSS CSS Box Model Reference

The overflow-x property specifies whether to clip content, render a scroll bar, or display overflow content of a block-level element, when it overflows at the left and right edges.

CSS CSS Box Model CSS Property Experimental Reference

The overflow-y property specifies whether to clip content, render a scroll bar, or display overflow content of a block-level element, when it overflows at the top and bottom edges.

CSS CSS Box Model CSS Property Experimental Reference