ConSentinel

Build a single self-contained `index.html` file — one full-viewport hero section for a
security product called "ConSentinel". No build step, no frameworks, no external JS.
All CSS in one `<style>` in `<head>`; all JS in `<script>` tags as described. Output the
complete file, nothing else.

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1. CORE CONCEPT — THE DESIGN-UNIT SYSTEM (do not substitute rem/px)
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The layout is a pixel-measured 1280×960 comp. Every size and offset is expressed in
`--u`, one reference pixel of that comp. The background plate stretches to the viewport
(never letterboxed) while every foreground element keeps its measured size.