Like I said, in HTML there are no things like circles or triangular shapes (or anything other that resembles a rectangular shape)
If you want to achieve such shapes, you should construct it by using multiple rectangular containers (FlexBoxes, MatrixLayouts, etc) or use the CSS3 "shapes" (https://css-tricks.com/examples/ShapesOfCSS/)
But using CSS for odd-shaped containers is a bit tricky... If there is no way you can convince your management that using odd shapes is a bad practice, I would go for the first approach instead