What do CSS transitions allow and how are they specified?

Explanation

CSS transitions smoothly animate changes to CSS properties over a specified duration. They are specified with transition-property, transition-duration, transition-timing-function, and transition-delay. Transitions trigger when a property changes (via hover, class toggle, etc.). Not all properties are animatable, but common ones include opacity, transform, color, and width. Transitions are more performant than JavaScript animations for simple effects. Use transform and opacity for GPU-accelerated animations.