I’ve found Furtive CSS really useful for my side-projects.
Although it offers few components, its clarity is straightforward.
Every width, height, etc is defined in rem. So, by updating the <html> element’s font-size, everything resizes perfectly on the fly.
On one of my last projects (which is an UI for my WordPress.com-based site) I had spent more than 80% of the time figuring out layout stuff.
A few nights ago, I branched the project into a <code>update/use-furtive-css</code> and it was amazing. In a few mins, everything looked clean as I was wishing.