[Webdev Live] Webinar 05: CSS Part 2 - Transforms, Transitions

in key frame crazy slide what is the meaning of 0%,50%,100% if animation-duration is 6s

These percentage in key frames means the same as normal percentage i.e. at 0% or start of animation, 50% or half of the time alloted for that animation here 3s and 100% means at the end of the animation.
You define the state here at these percentages and the rest is taken care by the key frames

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