After eight years of designing in the browser, this is a short list of things I believe to be true.

What good CSS does

• Doesn't break any functionality of plain html.
• Makes an interface more readable for everyone on any device.
• Enhances the usability of an interface for all devices.
• Allows you to quickly change a single interface without breaking other unseen interfaces.
• Renders quickly in the browser.
• Runs at 60fps (no jank on window resize or during scrolling).

What good CSS is

• Highly reusable - even across projects.
• Well documented.
• Easy to read and understand.
• ID free.
• Mobile-first.
• Easy to maintain.
• Very very small.
• Unassuming.