A Tiny RGB-to-Hex Colour Mixer

Goal Make one small offline colour mixer that exposes how three integer RGB channels form a hexadecimal colour code. Deliverable One self-contained UTF-8 HTML file, any descriptive .html filename, at most 22,000 bytes, opening locally without a server. Requirements 1. Provide three labelled numeric inputs for Red, Green, and Blue, initially 51, 102, and 153. Accept integers from 0 to 255 inclusive. 2. Update immediately to display the uppercase six-digit hexadecimal code with a leading #, a colour swatch, and each channel's two-digit hexadecimal value with leading zeros. 3. Blank, fractional, nonnumeric, and out-of-range inputs must show a useful inline error and clear the previous output and swatch. 4. Include visible reference examples: 0,0,0 = #000000; 255,255,255 = #FFFFFF; 51,102,153 = #336699; 0,15,255 = #000FFF. 5. Use labelled native controls, visible keyboard focus, and a polite live status. Display code and labels on a readable fixed background, so swatch colour never makes essential text unreadable. 6. Keep the layout usable at 360 and 1200 CSS pixels. Use ordinary sRGB channel values; no colour-management claims are required. Negative scope No reverse hex input, alpha channel, colour picker, palettes, contrast certification, file operations, clipboard, storage, network requests, external assets or libraries, tracking, accounts, or extra files. Pass/fail acceptance gates - One offline HTML within the byte ceiling, with three labelled inputs and the required outputs. - Correct zero-padding and conversion for all valid channel integers, including the four published examples. - Invalid input clears stale results; required accessibility and layout behavior is present. - No prohibited features or unsafe code. Scoring rubric (100 points, in order) 1. Correct conversion and input handling: 50 points. 2. Clear channel explanation and output: 20 points. 3. Accessibility and responsive layout: 20 points. 4. Readable code and visual polish: 10 points. Tie-breaker Prefer conversion and validation logic easiest to verify from readable code, then the clearest output. Styling is open. Judging uses this public brief and examples of the same stated rules, with no hidden features or filename requirements. One best valid submission receives the posted bounty after expiry, subject to marketplace fees.