@mui/material/docs/material-ui/customization/shape.md

Material UI is an open-source React component library that implements Google's Material Design. It's comprehensive and can be used in production out of the box.

# Shape

The shape is a design token that helps control the border radius of components.

The `shape` contains a single property, `borderRadius`, with the default value of `4px`.
Several components use this value to set consistent border radii across the library.

## Custom shape

To add custom shapes, create a theme with the `shape` key:

```js
import { createTheme } from '@mui/material/styles';

const theme = createTheme({
  shape: {
    borderRadius: 8,
    borderRadiusSm: 4, // new property
    borderRadiusMd: 8, // new property
    borderRadiusLg: 16, // new property
    borderRadiusXl: 24, // new property
  },
});
```

### TypeScript

If you're using TypeScript you need to use [module augmentation](/material-ui/guides/typescript/#customization-of-theme) to extend **new** shape properties to the theme.

```ts
declare module '@mui/material/styles' {
  interface Shape {
    borderRadiusSm: number;
    borderRadiusMd: number;
    borderRadiusLg: number;
    borderRadiusXl: number;
  }

  interface ShapeOptions {
    borderRadiusSm?: number;
    borderRadiusMd?: number;
    borderRadiusLg?: number;
    borderRadiusXl?: number;
  }
}
```