Space planet

Build a single, self-contained HTML file: a full-viewport space-themed hero section
for a site called "SpaceEdu". No build step, no frameworks, no external JS. All CSS in
one <style> block in <head>, all JS in one <script> block before </body>. It must be
pixel-faithful to the spec below and fully mobile responsive.

════════════════════════════════════════════════════════════════════════
1. CONCEPT
════════════════════════════════════════════════════════════════════════
A cinematic hero. A looping video of a single planet fills the whole viewport as the
background. Centred over it: eyebrow "PLANET", a huge serif planet name, a short cyan
rule, a paragraph, and a glossy white pill button. Flanking the button, cropped by the
left and right screen edges, sit two transparent planet cut-outs with serif labels.