Practical CSS: Combining :has, :not, :only-child and :placeholder-shown pseudo-classes

A practical guide to replacing JavaScript presentation logic with modern CSS pseudo-classes. Using a tag editor widget as a concrete example, it demonstrates how :only-child, :has, :not, and :placeholder-shown can handle dynamic UI states like showing/hiding elements, styling a single item differently, and toggling a clear button — all without touching JavaScript. The result is a simpler, more maintainable JS controller focused purely on functional logic, while CSS handles all presentation reactively.