Implement Bootstrap-like responsive utility classes

Implement a responsive grid layout and form using a Bootstrap-like utility-class approach without importing any external CSS frameworks. Define your own reusable CSS utility classes (e.g., container, row, col-*, spacing, typography) with mobile-first breakpoints, support nesting and gutters, and build accessible components such as a navbar, buttons, inputs, and validation messages. Provide the HTML/CSS (and minimal JavaScript if needed) to demonstrate responsiveness and semantic accessibility. As a follow-up, design robust error handling for invalid inputs and asynchronous form submission failures, including user-facing states (loading, success, retryable error, non-retryable error) and telemetry.