How to use css to bend the side of the block so that it resembles a T-shirt?

Question

css

Out of interest, I took up the site for ordering photographic souvenirs. I decided to use a minimum of pictures. I got the idea to make a page with the selection of the size.
I wanted to make her beautiful. I want to draw a T-shirt with css.
The blue part is just a block with rounded corners, the green (sleeves) - I'll think of something, they are not required, but desirable. If you know how to do it, write in the answer.
But the main problem is the notch (red), I don't understand how to make it. Help. Thank you.

Answer 1

Maybe not torturing css for such trifles and make a T-shirt in svg? Then you can use any css pranks - colors, line thickness and annoying T-shirt will look like a T-shirt :-)
And it will be easier to finish something.