Kilian Valkhof

Building tools that make developers awesome. 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.

Detecting media query support in CSS and JavaScript

CSS & HTML, Javascript, Web, 13 July 2021

Recently I needed a way to detect support for a media query in CSS and Javascript. To detect if a browser supports a certain CSS feature, you can use @supports () { ... }, but that doesn’t work for media queries. In this article I’ll show you how you can detect support for media queries regardless of if they are turned on.

Increasing access to your website with “prefers-reduced-data”

Accessibility, 12 July 2021

The upcoming “prefers-reduced-data” media query will make your site more accessible in the “more people can now enter the building” meaning of accessibility. In this recording of my talk given at Shortstack conference you will learn strategies to start implementing this feature now and make your site available to even more people.

Fixing contrast issues, on your own site and elsewhere

Accessibility, 8 June 2021

Insufficient text contrast is the most common accessibility issue on websites today. According to the WebAIM Million report for 2021, 86.4% of home pages world wide have low contrast text. What’s worse, this number has been increasing the past three years.

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


A cross-platform, simple and smart autosaving scratchpad.

A Messenger Adventure!

Go on a text adventure in Facebook Messenger.


The latest Electron news, articles, apps and interviews.


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

Messenger Demo Viewer

Demo your (bot) interactions on Messenger.