Make an animated glowing border effect with CSS

A comprehensive tutorial demonstrating how to create an animated glowing border effect using pure CSS, inspired by Google's AI search interface. The technique uses conic gradients, pseudo-elements, and CSS custom properties to achieve a dynamic glow that works with any background color and supports both light and dark themes. The implementation includes positioning tricks with z-index and stacking contexts, blur filters for the glow effect, and registered custom properties for smooth animations. The tutorial also covers creating variants for different border positions and making the effect easily customizable through CSS variables.