Gotcha. That’s because of the 100% vs auto thing. These days everyone just puts “box-sizing: border-box” on everything to make it go away. This explains a bit

Gotcha. That’s because of the 100% vs auto thing. These days everyone just puts “box-sizing: border-box” on everything to make it go away. This explains a bit more about what you’re seeing http://stackoverflow.com/questions/28353625/why-does-percentage-width-work-even-if-no-explicit-width-value-given-for-contain/28354270#28354270 http://stackoverflow.com/questions/28353625/why-does-percent...