https://codepen.io/Ariex/pen/.
uses background-blend-mode: overlay; so IE and Edge users won't see it, but it doesn't matter. Anyway, IE has been thrown into the trash, and Edge will soon be replaced by MS with chromium

Thank you for the invitation.

you can use border-radius to achieve reverse fillet. The principle can be found in my previous article using pure css to achieve a coupon

compatible with all browsers that support rounded corners

border:500px solid red;//

here is the implementation of demo

https://codepen.io/xboxyan/pe.

roughly implements

svg, compatibility should be fine
https://jsfiddle.net/3j6uehLy/1/

border-radius:0px 34px 34px 0px;
overflow:hidden;

this doesn't work in a translucent background color. Please refer to @ Xeira's answer

border-radius is similar to drawing a circle for OK,.