Industrial-Styled Login Page Design

I need a compact and visually strong login page built using vanilla HTML, CSS, and JavaScript.

The design should be inspired by an industrial look similar to Caterpillar equipment—using a dark (black/charcoal) background, bold yellow accents, and subtle grey tones. Please do not use any logos or images—only colors and styling.

Requirements:

HTML

- Form with "id="login""
- Username input with "id="name"" and attribute "data-defaultuser="admin"" (this value should be flexible)
- Password input with "id="password""
- A single reusable error container: "id="error""

CSS

- Clean, modern UI with strong contrast
- Caterpillar-inspired color palette (yellow, black, grey)
- Compact and responsive layout
- Smooth focus/hover states for inputs and button

JavaScript

- Validate both fields on form submission
- Show error messages inline (below inputs)
- Use the "#error" element for displaying messages
- Errors should disappear automatically when corrected
- No alerts, popups, or external libraries
- On successful validation, log success or include a placeholder redirect

Deliverables:

- "index.html"
- "style.css"
- "script.js"
- A short README explaining how to change the default username

Code should be clean, well-commented, and easy to maintain.

Looking for quick delivery and good UI sense.