CSS display

The CSS display module defines how the CSS formatting box tree is generated from the document element tree and defines properties controlling it.

Reference

Using the multi-keyword syntax with CSS display: Describes the multi-keyword syntax and compares this syntax with legacy single-keyword values.
Block and inline layout in normal flow: The basics of how block and inline elements behave when they are part of the normal flow.
Flow layout and overflow: How overflow works when working with normal flow.
Flow layout and writing modes: How flow layout behaves when used with different document writing modes.
Introduction to formatting contexts: Formatting contexts, including block, inline, and flex, their behaviors, and use.
In flow and out of flow: What takes elements out of flow, and the effect of creating new Block Formatting Contexts.

Specification
CSS Display Module Level 3