If you are a web designer from the 90's (like someone I know), you are familiar with ribbons and banners. If you are a web designer in the 21st century, you hate how hokey they are. Sometimes they may still be used to get the point across, so it's important that they work on every device. Here are some responsive ribbons using CSS and a little trigonometry.
Original design by Temani Afif for Smashing Magazine.
Read the 2-part article for a comprehensive explanation.
No way was I going to recreate the math. I hurt myself just reading it.