Kilian Valkhof

Building tools that make developers awesome.

Comparing CSS Specificity values

CSS & HTML, Javascript, 17 January 2022

CSS Specificity is usually written out as [a,b,c] for ID’s, classes and elements respectively. Even a single ID is more specific than any number of classes or elements, so it’s displayed as an array and can’t really be fitted into a single number. How do you compare two selectors to decide which has the highest specificity?

Your CSS reset needs text-size-adjust (probably)

CSS & HTML, 7 January 2022

I don’t get to work on a lot of new sites nowadays, but I recently got the opportunity to set one up from scratch. For most sites I built when I was still running an agency, I would use some form of CSS Reset, most often Normalize.css, but I figured that this time round I could do with a few basics, like box sizing and resetting margins on the body, and call it a day.

WCAG 2 is what we have

Accessibility, 13 December 2021

Last week, I got tagged twice in a Twitter thread about the new APCA color contrast algorithm, asking my opinion and when it was gonna appear in Polypane (it will). APCA has a lot of developers and designers excited, because its a much more thorough algorithm for color contrast compared to the algorithm currently in WCAG 2. podcast recording on Polypane, Electron, Superposition

CSS & HTML, Electron, Web, 4 November 2021

I recently sat down with the folks at to talk about my experiences as an indie developer building Polypane and Superposition, my experience working with Electron and my thoughts on the framework, and on FixA11y, the browser extension I’m building in my spare time. Listen to it below:

CSS Nesting, specificity and you

CSS & HTML, 4 August 2021

Native CSS nesting is coming to browsers soon. With nesting, that you might be familiar with from Sass or Less, you can greatly cut down on writing repetitive selectors. But you can also really work yourself into a corner if you’re not careful. This is an overview of how you can already use it today, the pitfalls and how to avoid them.

Polypane browser for responsive web development and design Hi, I'm Kilian. I make Polypane, the browser for responsive web development and design. If you're reading this site, that's probably interesting to you. Try it out!

I develop more software and tools:


Use the design system you already have


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Drag-and-drop lossless compression of PNG and JPG images for web.

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Demo your (bot) interactions on Messenger.