Before I get into the tech: the atmosphere and the sheer passion of everyone there is fantastic. What makes CSS Day so special is that you actually come into contact with people from the CSS Working Group, MDN spec writers, and folks working on HTML, JavaScript and the browsers themselves. It is so cool to be able to meet the people who build the technology we use every single day.

CSS Day 2026 in Amsterdam was two weeks ago and I still cannot get it out of my head. Here are the techniques that stuck, the ones I actually want to use.

Color

  • Work in oklch() for predictable, perceptually even colors. Mixing and lightening hex values is why you keep getting mud.
  • Build palettes generically and use chroma clipping to keep them in gamut instead of hand-picking hex values.

Text size and user preferences

  • Use rem, but never set a root rem yourself. The browser preference owns it, and overriding it breaks the user's OS text size (which roughly a third of phone users change).
  • New env values expose the OS text scaling.
  • Do fluid type and spacing properly. utopia.fyi is the reference.
  • Treat prefers-* (dark, light, contrast, reduced motion) as instructions, not edge cases.

CSS replacing JavaScript

  • Advanced attr(), style queries and if() let CSS read and interpret values. JS just fetches data and hands it to CSS.
  • popover, commandfor, anchor positioning with position-try and flip rules, calc-size() and appearance: base-select replace most menu, tooltip and custom-select libraries.

Motion

  • View transitions: morph between elements with view-transition-name, animate across pages with @view-transition, no framework needed.
  • Scroll-state queries let an element react to being stuck or scrolled. This replaces a lot of janky scroll JavaScript.

Theming

  • color-scheme, light-dark() for specific elements, and system colors give you light and dark without override soup.

Performance

  • content-visibility skips rendering offscreen content until needed. Low effort, high impact on long pages and heavy canvases.

Worth bookmarking

For the full speaker line-up and the talks, check cssday.nl.