What's New in CSS #1: progress() is coming to Firefox, CSS Mixins, and CSS breakpoints used by popular frameworks
The first CSS-Questions weekly roundup covers CSS progress() function coming to Firefox, CSS Mixins, and CSS breakpoints used by popular frameworks
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Technical writer and software engineer making CSS easier to understand through practical explanations, questions, and games.
CSS has been advancing over the past few months, and I decided to write a little about what’s new this past week. From the CSS progress() function coming to Firefox, making it a Baseline feature, to CSS Mixins coming to CSS, changing the declarative programming language forever, and finally to CSS breakpoints used by popular frameworks, here’s a breakdown of CSS’ latest updates you missed last week on What’s New in CSS #1!
progress() is coming to Firefox
As of this writing, browser support for the CSS progress() function is stable across all major browsers except Firefox, but this is about to change because on July 25th, 2026, the Mozilla team have expressed their intention to release the CSS function to Firefox. As to when this will happen, the honest answer to that is, I don’t know. It depends on the next Firefox release, but I don’t see on Firefox 154 Beta, nor is it present in Firefox 155 Nightly. The team did mention that they intend to publish it on Firefox 155. BUT, we will wait and see. On the bright side, even though the no-clamp keyword was recently added to the CSS Values and Units Module Level 5, Safari has already implemented the keyword for the progress() function in Safari Technology Preview 248 (which is very fast by the way). They are, in fact, the first browser to implement this keyword for the CSS function.
Sources
- Intent to Ship: CSS
progress()function — Mozilla dev-platform progress()CSS function — MDN Web Docsprogress()notation — CSS Values and Units Module Level 5- Safari Technology Preview 248 release notes — WebKit
CSS Mixins are here (almost)
I first saw this news from Dr Lea on Bluesky and went ahead to do my own investigation on what’s coming:
It’s looking like Microsoft Edge may be the first browser to bring this feature to native CSS, and I’m really excited about this. Well, mainly because it helps with DRY (Don’t Repeat Yourself) code and it’s been an anticipated feature for a long time. Geoff Graham has some helpful notes on this.
Sources
- Intent to Prototype: CSS mixins — Chromium blink-dev
- CSS Custom Functions and Mixins Module Level 1 — CSS Working Group
- CSS Functions and Mixins Module Notes — CSS-Tricks
CSS breakpoints used by popular frameworks
Polypane Blog shows us a nice overview of all breakpoints used by our popular FE frameworks such as Bootstrap, TailwindCSS, and a lot more. At least, with this article, you get to know that not all “md” inherently means tablet size; instead, you get to understand that a specific width variable is assigned to a particular framework, and you can decide which one works best for you or tweak your favorite framework’s breakpoints as you see fit.
Source
Introducing Weekly Review Tests!
Yes! You read that right! I was thinking, “What would make us different from every other blog?” I thought long and hard about it and defaulted back to why I created CSS-Questions, simply to make learning and CSS recall fun. And what better way to end our CSS-WR with a simple quiz on what was discussed during the week to make it stick. You simply answer 5 questions based on what was discussed, and then if you pass, congrats! If there are some you missed, I advise you to come back, reread the parts you missed and start the test again. Don’t worry, this is not a timer-based test. You get to take your time with these so you can understand them better.
Without further ado, here’s the quiz for this week!