GPT-5.3-Codex vs GPT-5.5 for vibe coding

- Add labels for bill and tip fields to improve accessibility.
- Validate bill is a non-negative number; show helpful error when invalid.
- Use `document.getElementById` in `calc()` instead of implicit global element variables.

```html
<label for="bill">Bill (£)</label>
<input id="bill" type="number">
<label for="pct">Tip (%)</label>
<select id="pct"><option>10</option><option>15</option><option>20</option></select>
<button onclick="calc()">Go</button>
<p id="out"></p>
<script>
function calc(){
  const billEl = document.getElementById('bill');…

- Add labels and live output for better accessibility.
- Validate non-negative bill amounts before calculating.
- Replace inline click handler with scoped event listener.

```html
<label for="bill">Bill</label>
<input id="bill" type="number" min="0" step="0.01" required>

<label for="pct">Tip %</label>
<select id="pct">
  <option>10</option>
  <option>15</option>
  <option>20</option>
</select>

<button id="calcBtn">Go</button>
<p id="out" aria-live="polite"></p>

<script>
const billEl = document.getElementById('bill');
const pctEl = document.g…