How might I force a floating DIV to match the height of another floating DIV?

Question

My HTML code is just dividing the pages into two columns, 65%,35% respectively.

Answer 1

Flex does this by default.

CSS:

#flex{display:flex}
#response{width:65%}
#note{width:35%}

https://jsfiddle.net/784pnojq/1/

BONUS: multiple rows

https://jsfiddle.net/784pnojq/2/