PUBLIC MARKS from decembre with tag csstricks

(Better) Tabs with Round Out Borders We'll show how you can use the CSS :before and :after pseudo elements to create a rounded bottom border edge for each tab without using images.

calc() is a native CSS way to do simple math right in CSS as a replacement for any length value (or pretty much any number value). It has four simple math operators: add (+), subtract (-), multiply (*), and divide (/). Being able to do math in code is nice and a welcome addition to a language that is fairly number heavy. But is it useful? I've strained my brain in the past trying to think of obviously useful cases. There definitely are some though.