I find mobile-first development easier. Every time I design a UI for a desktop first, it's slightly broken on mobile. It's easier to scale up than down.
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You can often estimate the age of a website based on how well it displays on mobile.
All my sites end up with media queries in the CSS for narrow screens. It's so hard to design a single UI that scales from phone to desktop otherwise.
It's weird that GitHub shows time since the last commit, but not time since the first commit. It's a nice way of seeing how mature a project is.
Here's a weird UI pattern I haven't seen before. This sanitizer will keep things clean for 24 hours, so the time counts *down*.
Every time I see it, it looks like 24 hour clock showing the wrong time!