# Fast and Reliable CSS

Fast and Reliable CSS: Will It Work Everywhere? Browser Support and @supports, CSS Performance: What Slows a Page, and Critical CSS.

Updated: November 10, 2026

1. [Will It Work Everywhere? Browser Support and @supports](https://www.ask-codey.com/lessons/css-browser-support) (Journeyman): Check whether a CSS feature works in your readers' browsers with Baseline and caniuse.com, then use it safely with fallbacks the cascade gives you for free, @supports, and progressive enhancement.
2. [CSS Performance: What Slows a Page, and Critical CSS](https://www.ask-codey.com/lessons/css-performance) (Freelancer): See why a stylesheet holds up the first paint, find unused CSS with the Coverage panel, animate transform instead of layout, skip off-screen work with content-visibility, inline the critical CSS, and measure the result with Lighthouse.

Source: https://www.ask-codey.com/courses/css-in-depth/topics/css-fast-and-reliable-css