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Colors:

how do we decide where to use custom properties? There are really two cases:
1) whenever we need to use the same value in more than one place (DRY)
2) when we know a value is going to be changed.

Custom Properties:

I already use the css variables methods. They are great. Note we can inline them and avoid a verbose default: var(--btn-color, var(--color-text))

You can think of :has() as a way to query an element about what’s inside it.

This makes our button class very flexible. You can throw about any combination of things inside it, and it will adjust accordingly. Text only, image and text, image only, inputs (like radio buttons), or multiple images with text.

The post of 37signals takes also the sidebar into account. The trigger button can be pure CSS even if the icon in it changes. :has() allow to verify if a button inside an element is disabled too.

Responsive design:

They use one @media breakpoint (max-width: 100ch) for a two column layout.

Using characters as the unit of measure ensures that we get the right behavior no matter which device you’re using and in a number of other scenarios such as multitasking on iPad or even if you simply enlarge the font size past a certain point. Type is the heart of web pages so it makes sense for the layout to respond to it.

Feature enhancements such as hover or touch effects with media queries: @media (any-hover: hover) in combination with (pointer: fine) or (pointer: coarse)

Great stuff and kudos to them 👏

with currently 90% support, this feature can render or hide the content (without taking space in the layout). Note the auto value can optimize the rendering

In comparison with the display: none trick, developers don't need to specify the layout display: flex | grid | block anymore.

Are they useful? I think not. It might be useful, but overall, it's better to read the specifications.

Following https://dev.37signals.com/modern-css-patterns-and-techniques-in-campfire/

More thoughts about utility classes (only utilities and not a core use anymore), :has(),

What fascinated me most was watching the architecture evolve across releases.

Campfire: OKLCH colors, Custom properties for everything, character-based spacing, flat file oranization, View Transitions API
Writebook (2nd): COntainer queries for component-level responsiveness, @starting-style for entrance animations
Fizzy (3rd release): CSS Layers, color-mix() and complex :has() to replace JS.

37Signals share their product codes in Open Source. That's awesome because we can learn from it:

/* Fizzy's layer architecture */
@layer reset, base, components, modules, utilities;

@layer components {
  .btn { /* Always lower specificity than utilities */ }
}

@layer utilities {
  .hide { /* Always wins over components */ }
}

A CSS only spinner under 30 lines of CSS code. "Pure creativity".
A better <mark> that draws a hand-drawn circle around matched terms.
They also created dialog animations in CSS only.

They are CSS "cascading" variables, and they can also be custom properties with @property.

* {
  letter-spacing: clamp(
    -0.05em,
    calc((1em - 1rem) / -10),
    0em
  );
}

Some creative ideas on small screens. The post lists examsle:

• Use horizontal scrolling
• Push elements off-canvas
• Build scrollable mini-spreadspread
• Orientation responsive layout

An example of semantic class names and a teaser on server of Kelp to have dynamic HTML through WebComponents.

Waayyy tooo coool checkboxes as switch

How CSS simplify scrollable images with

display: flex;
overflow-x: auto;
overscroll-behavior-inline: contain;
scroll-snap-type: inline mandatory;
scroll-behavior: smooth;

// On the images
scroll-snap-align: center;
 contain: size;
  place-self: stretch;
  object-fit: cover;

Tips and tricks for view transition

In my opinion, the best cases for implementing view transitions are as a way to draw attention to an element, convey movement, and help users remain in context.

Add it to all pages to apply a default cross fade transition.

@view-transition {
    navigation: auto;
}

Then mark similar content with the view-transition-name css property.

Custom view transitions can be made with ::view-transition-old, ::view-transition-new, ::view-transition-image-pair.
Full page transition can be done by marking :root.
These transitions should be set only when the media query prefers-reduced-motion is set to no-preference.

Use cases for inherit(). They can be good but I don't see a need currently

There are great animations of ease-in, ease-in-out, ease, spring and bounce. The latest two can not be animated with Bézier curves as other common animations.

To get spring and bounce effects, the linear() function can be used. The linear() function takes a set of numbers, with 0 representing the starting value and 1 representing the final value.

Easing wizard or the Linear() Easing Generator can help.

If JS fails to load, a keyframe remove the effect provided by JS in 2 seconds.