Modern CSS Best Practices

What this best practices guide is

A practical guide to writing CSS that scales, checked against MDN, web.dev Baseline, the W3C accessibility guidelines and the Tailwind CSS docs. It covers controlling the cascade with layers, design tokens in custom properties, modern layout, responsive and container based design, :has() and native nesting, accessibility and motion, and using Tailwind CSS v4 well.

It has 9 chapters and 37 practices, each with why it matters, what to do and what to avoid. For frontend and full stack developers.

Chapter by chapter

1. Foundations: support, units and a sane base (4 practices)

Before writing component styles, decide which features you can rely on, how you size things, and what every element starts from.

2. The cascade, specificity and cascade layers (4 practices)

Most CSS pain comes from styles fighting each other. This chapter covers keeping specificity low and using cascade layers to decide which group of styles wins.

3. Custom properties and design tokens (4 practices)

Custom properties turn colours, spacing and type into named, themeable values. This chapter covers organizing them as tokens, scoping, fallbacks and typed properties with @property.

4. Layout with Grid and Flexbox (4 practices)

Grid and Flexbox replace floats, positioning tricks and most layout media queries. This chapter covers choosing between them and the patterns that make layouts adapt on their own.

5. Responsive design (5 practices)

Responsive design is about content working at every size and zoom level, not about a few device widths. This chapter covers mobile first styles, breakpoints, fluid type and reflow.

6. Container queries (4 practices)

Container queries let a component respond to the space it is given rather than the size of the window. This chapter covers setting up containers, querying them and container units.

7. Modern selectors and native nesting (4 practices)

:has(), :is(), :where() and native nesting remove many reasons to reach for JavaScript or a preprocessor. This chapter covers using them well and their traps.

8. Accessibility, focus, colour schemes and motion (4 practices)

CSS decides whether people can see where they are on a page, read the text and use it without discomfort. This chapter covers focus styles, reduced motion, colour schemes and hiding content correctly.

9. Using Tailwind CSS well (4 practices)

Tailwind CSS v4 is built on the same modern CSS: cascade layers, custom properties and container queries. This chapter covers theme tokens, class detection, custom CSS and responsive variants.

How it works on Sefism

The guide reads like a short course: a syllabus, then one chapter per page in a focused reader, with a quiz at the end of each chapter for members. The opening chapters are open to everyone. Adding it to your account uses credits, opens every chapter and keeps your progress.

Every claim is checked against the sources listed on the page (8 cited).