.css-day {
  date: 'June 8 & 9';
  speakers: 14; // Single-track
  venue: Zuiderkerk; // Amsterdam, NL

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CSS Day started out in 2013 as a single-day, laser-focused, advanced CSS conference, and we started intertwining design sessions a few years ago. Our attendees and speakers are a mix of CSS designers, developers, spec writers and browser vendors, who take pride in what they know and do. We're a conference with an informal vibe and plenty of breaks, where each person can approach one another.

This year, we'll have 14 speakers, covering these topics:


Adam Argyle

Adam is a bright, passionate, punk engineer with an adoration for the web who prefers using his skills for best in class UI/UX and empowering those around him. He’s worked at small and large companies, and built an app for pretty much every screen (or voice). He is capable of over-engineering, but spends lots of brain power not. Loves CSS, loves JS, loves great UX.

Shining Light on the Shadow DOM

Light DOM, Shadow DOM, encapsulation, slots, templates — vocabulary gets thrown around a lot when we talk about styling Web Components but how do all these pieces fit together? It’s easy to get caught up in the JavaScript of it all but in this talk, we’re going to dig into the nuances of styling these darlings of design.

Together we’ll examine the cascade and learn how inheritance works when Shadow DOMs get involved. After a crash-course in terminology, we’ll explore some of the “gotchas”, look at browser inconsistencies, and I’ll proffer some compatibility approaches that won’t give you a migraine. We’ll wrap things up by zooming out and examining how we can use Web Components to build consistency in a codified design library through theming.

Cassondra Roberts

Cassondra (aka castastrophe) is a design systems engineer for Adobe and member of the CSS Working Group. At Adobe and before that, Red Hat, her work involves collaborating with designers on building scalable systems; recently leveraging Web Components to build theme-able assets to be consumed in diverse contexts. More than anything, Cassondra cares about creating a free and open web that is accessible to all. She’s currently putting the finishing touches on a comprehensive guide to styling Web Components.

Heydon Pickering

Heydon is a technical writer, frontend developer, and video producer. They co-wrote Every Layout with Andy Bell—the release of which first being announced at this very conference! Heydon likes CSS algorithms, baritone guitars, and generative art.

View Transitions

Jake Archibald

Jake works on web standards stuff for Google Chrome (for now at least), focusing on performance, and making the web more competitive with native platforms.

Jhey Tompkins

Jhey brings ideas to life with code! Branded as a whimsical specialist, he shows people how to level up using creative coding on the web platform via the “Impractically practical”. He advocates for creative coding giving you the confidence to build anything you can imagine.

Structuring & Restructuring

Manuel Matuzović

Manuel Matuzović is a freelance frontend developer, accessibility auditor, teacher, and consultant who’s passionate about the web. He writes about accessibility, HTML, and CSS on his personal blog matuzo.at and on htmhell.dev.


Michelle Barker

Michelle is a Senior Front End Developer at Ada Mode, where she builds web apps for the renewable energy industry. She’s the author of front-end blog CSS { In Real Life }, and a Mozilla Tech Speaker. She has written articles for CSS Tricks, Smashing Magazine, and Web Designer Magazine, to name a few. She enjoys experimenting with new CSS features and helping others learn about them.

CSS Containers, What Do They Know?

A deep-dive introduction to CSS Container Queries

How did Container Queries go from ‘impossible’ to ‘shipping’ after so many years? How do we use them, and what hidden powers do they have? What are CSS containers, and what queries can they respond to? Let’s find out!

While the basics look a lot like media queries, and can work as a drop-in replacement for many existing @media rules — there are some key differences to understand, and a lot more power than you might expect. Along the way we’ll encounter CSS fundamentals like normal flow, intrinsic and extrinsic sizing, value resolution, and more. Join me to learn all you need to know about using container queries in your web projects.

Miriam Suzanne

Miriam is an artist, engineer, and open-web advocate. She’s a co-founder of OddBird, Invited Expert on the W3C CSS Working Group, and Sass core contributor who enjoys pushing the boundaries of web technology.

These days she’s working on specifications for Container Queries, Scope, and Cascade Layers in CSS; extending the Sass color module to support wide-gamut colors; and learning to crochet socks.

Style Recalculation Secrets They Don't Want You To Know

A deep dive into style recalculations and CSS selector performance

How do browsers actually recalculate styles when webpages change? Can the way you write CSS impact the speed of the recalculation process?

In this talk, we'll go through the details of how browser engines react to DOM changes and apply styles to the page again. We'll also take a look at examples and case studies to make things practical. And finally, we'll review developer tools that will help you investigate style performance bottlenecks.

Patrick Brosset

Patrick has been working with web technologies for over 2 decades. He has built websites and apps, libraries and open-source frameworks, and has worked on both Firefox and Chromium DevTools.

Patrick currently works at Microsoft as a developer relations PM on the Microsoft Edge team. He is passionate about the web platform, PWA, and DevTools, and writes a lot of articles about it at on his blog, css-tricks, smashing magazine, and others.

Tinkerer by Night

As a designer I try to be a master of my chosen medium – CSS and HTML with a whiff of JS. No better way to explore the possibilities of CSS by stretching it to the max. Throw your certainties out of the window and start experimenting with new, elegant and joyful ways to design and code the Web. Sometimes a success, just as often a total fiasco – but always educational, humbling and fun! This live-coding session pays homage to utterly useless side projects and to why they are important for my digital design students as well.

Sanne 't Hooft

Sanne is a seasoned lecturer at the Hogeschool van Amsterdam. His specialties include interaction design and code for digital design students. Until now 5793 (and counting…) students have had the pleasure ;-) of attending one of his courses. In a past life Sanne used to be an interaction designer of large complex functional applications. As part of that job, he created lots and lots of prototypes to test new interaction design ideas using actual code. Nowadays his code tinkering (which is limited to utterly useless side projects) is always fun (and educational), allowing him to push the capabilities of CSS and keep his coding skills sharp.

Practical Accessibility

Sara Soueidan

Sara is an independent inclusive design engineer, author, speaker, and trainer from Lebanon.

She is the author of the Codrops CSS Reference and co-author of Smashing Book 5 — a book that covers time-saving, practical techniques for crafting fast, maintainable and scalable responsive websites. She blogs about design engineering and her experience as a design engineer on her blog sarasoueidan.com/blog. Sara has been published on publications including net Magazine, Smashing Magazine, A List Apart, Codrops, CSS-Tricks, and more.

This Talk Is Under Construction: A Love Letter to the Personal Website

Remember Geocities? The unbridled creativity and questionable colour schemes of a bygone era. There was a time when websites existed as reflections of your personality or a shrine to your favourite band rather than carbon copies of a Facebook page or Twitter feed. Content wasn’t algorithmically curated, but shared through links pages and webrings.

With today’s browsers and modern CSS, we have at our fingertips so many powerful APIs and tools to build the most incredible, beautiful and wonderfully pointless websites that have ever existed, in ways that are accessible and performant like never before. And in the wake of Twitter’s slow demise, the humble personal website is rising from the ashes.

This is a manifesto for building something just for the fun of it, and a rallying cry to tell your story on a platform that’s entirely yours.

Sophie Koonin

Sophie is the web engineering lead at Monzo Bank in London, responsible for the web platform across the organisation and working on internal tooling that powers Monzo’s award-winning customer service. Building websites since the age of 10, she’s passionate about creating inclusive, accessible and fun websites that people love. Sophie writes about tech & mental health at localghost.dev, builds intentionally useless web apps, and makes music.

Stephanie Eckles

Stephanie is a front-end-focused SWE at Microsoft. She’s also the author of ModernCSS.dev which provides modern solutions to old CSS problems as in-depth tutorials and is the creator of StyleStage.dev, and author of SmolCSS.dev and 11ty.Rocks. Steph has well over a decade of webdev experience that she enjoys sharing as an author, egghead and workshop instructor, Twitch streamer, and conference speaker. She’s an advocate for accessibility, scalable CSS, and the Jamstack (especially Eleventy). Offline, she’s mom to two girls and a cowboy corgi and enjoys baking.

Stephanie Stimac

Stephanie is a Developer Experiences Product Manager with a background in design and development. She is currently a Senior Product Manager at Rapid, where she builds developer tools for APIs, and is the author of “Design for Developers” that teaches developers design fundamentals in the context of the web. Previously, Stephanie worked on the Microsoft Edge team for six years designing DevTools, shipping browser features, and leading DevRel. Her experience has given her a deep understanding of developers, their pain points, and the intersection of design and development.

Modern CSS Development and Debugging

In this session, you'll learn how to use modern tooling to your advantage when working on CSS code. Quickly scaffold out your project, use code snippets in any context, setup powerful editor workflows, and more. You'll also learn about tools that can help with CSS performance and visual regression testing, so you can confidently change your code while trusting the process!

Umar Hansa

Umar is a front-end web developer, public speaker and content creator based in London. Umar has a focus on writing tips, tutorials and documentation for the modern web platform. One of the projects he plans to explore and share with the community is using modern tools and technologies for a better development and debugging workflow.

Una Kravets

Una is a Developer Relations Engineer at Google Chrome where she leads the Web UI & DevTools DevRel team. Previously, she was the Director of Product Design at Bustle Digital Group and worked on building maintainable design systems as a UI Engineer at DigitalOcean and IBM. Una is the co-host of the CSS Podcast and Designing in the Browser video series. She has built open source libraries such as CSSgram, spoken at over 80 developer events around the world, and is an avid calligrapher/doodler.

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“The CSS Day organisers have once again set the bar very high for the next edition, let’s hope there will be another one in 2020!” — Hidde de Vries