CSS element with curved bended border/edge or line

I would like to create curved/bended shapes for my containters and also as a individual separators/elements. Here is the example: https://imgur.com/26mQYEs please look at the blue shape(I know this is not sharp but this is only a fast example)

How I can create effect like this one in 2019 and make this responsive? What methods, elements and tools I should use? Could you please give me examples?

Of course I want to make this solution responsive.

I have no idea how to do it, of course I can cut this as jpg image from photoshop but it will be not responsive.