Cordex

Build a single self-contained file `index.html` (no build step, no frameworks, no external JS libraries — one HTML file with an inline `<style>` and an inline `<script>`). It is a scroll-driven product landing page for a cable-protection brand called "cordex". Reproduce it exactly as specified below.

=====================================================================
0. THE ONE THING THAT MAKES THIS FEEL RIGHT
=====================================================================
The hero is a video scrubbed by scroll position. That only feels smooth if the MP4
is encoded ALL-INTRA (every frame a keyframe), because each scroll frame seeks to a
new time and a normal long-GOP encode must decode forward from the previous keyframe.
The URL given in section 7 is already encoded this way:

  145 frames / 145 keyframes, H.264 High profile, yuv420p, 1928x1076, 24 fps,
  6.04 s, 6.2 MB, 8.6 Mbps, faststart, no `stss` box (absent stss == all frames