Build a step-by-step interactive explainer web app that teaches a beginner how to choose an LED's series resistor

# Build a step-by-step explainer web app: choosing a series resistor for an LED Make a small interactive web app that teaches a beginner one hardware topic, one step at a time: how to pick the series resistor for an LED. `spec.json` gives the page title, the steps (each with a title and a fact sentence), and the standard resistor series to use (`series_base`, one decade of values, repeated across `decades`). Look, layout and wording beyond the spec are up to you; **looks are not scored**. The page is scored in a headless browser (800x600 window, network blocked) by objective checks only. Write one file, `out/explainer.html`, that works opened straight from disk. ## Steps - Show one step at a time. On load, step 1 is shown. Put the current step's title in `#step-title`, its text in `#step-body` and a counter in `#step-count`. - Buttons `#prev` and `#next` move one step back or forward. - Every step title must appear in `#step-title` in the order given in spec.json, and `#step-count` reads "Step <i> of <N>". - `#prev` is disabled (the `disabled` property) on step 1 and `#next` is disabled on the last step; neither moves past the ends. - `#step-body` for each step contains that step's fact sentence from spec.json exactly as written (extra text around it is fine). ## Calculator Inputs `#in-supply` (supply volts), `#in-vf` (LED forward volts), `#in-ma` (LED current in mA) and `#in-count` (LEDs in series, a whole number); outputs `#out-ohms`, `#out-standard`, `#out-mw` and `#out-error`. The calculator is visible on every step and recalculates on each `input` or `change` event (a `#calc` button is optional; it is clicked too if present). - For supply V, forward voltage F, current I mA and count n: R = (V - n x F) / (I / 1000). `#out-ohms` shows R rounded half-up to a whole ohm. - `#out-standard` shows the smallest standard series value that is at or above the exact R, never a smaller one. - `#out-mw` shows the resistor's power, (V - n x F) x I, in mW rounded half-up to a whole number. - Show numbers as plain digits (for example `1200`, not `1.2k`); a unit after the number is fine. - If any input is missing or not positive, or V is not greater than n x F, `#out-error` shows a non-empty message and `#out-ohms`, `#out-standard` and `#out-mw` are empty. Otherwise `#out-error` is empty. ## Checks (partial credit = share passed) 1. `self_contained`: `out/explainer.html` exists, is at most 150,000 bytes, references no http(s) or protocol-relative URL, and requests nothing from the network when opened. 2. `required_elements`: every element id named above is present, and the `<title>` contains spec.json's `title`. 3. `steps_in_order`: Every step title must appear in `#step-title` in the order given in spec.json, and `#step-count` reads "Step <i> of <N>". 4. `navigation_limits`: `#prev` is disabled (the `disabled` property) on step 1 and `#next` is disabled on the last step; neither moves past the ends. 5. `step_facts`: `#step-body` for each step contains that step's fact sentence from spec.json exactly as written (extra text around it is fine). 6. `calculator_values`: on hidden test inputs, `#out-ohms`, `#out-standard` and `#out-mw` all match the rules above. 7. `invalid_input`: If any input is missing or not positive, or V is not greater than n x F, `#out-error` shows a non-empty message and `#out-ohms`, `#out-standard` and `#out-mw` are empty. No build step and no other files are scored. ## How this run works - Work on your own: nobody will answer questions in this task, and writing to `ask/` counts against the run. - Write only under `out/`. Create `out/` if it is missing. Inputs are synthetic; don't fetch anything from the network. - Scoring is partial credit: each listed check is pass/fail, and the score is the share passed. Numbers are compared to within 0.005 unless the task says otherwise.