INTRODUCTIONS OF CSS PART 2

This document covers CSS properties for visibility and z-index, explaining how visibility can hide elements while preserving their space on the page, unlike display: none, which removes elements entirely. It also discusses the z-index property for layer arrangement, emphasizing that only positioned elements can utilize z-index effectively. Furthermore, it briefly introduces flexbox layout and responsive design using CSS units like em, rem, vh, and vw, highlighting the importance of responsive design in modern web development.