React

HTML

<div id="app"></div>

CSS

body {
  background: #fff;
  padding: 20px;
}

React

const Rect = ({width, height, tl, tr, br, bl}) => {
    const top = width - tl - tr;
    const right = height - tr - br;
    const bottom = width - br - bl;
    const left = height - bl - tl;
    const d = `
        M${tl},0
        h${top}
        a${tr},${tr} 0 0 1 ${tr},${tr}
        v${right}
        a${br},${br} 0 0 1 -${br},${br}
        h-${bottom}
        a${bl},${bl} 0 0 1 -${bl},-${bl}
        v-${left}
        a${tl},${tl} 0 0 1 ${tl},-${tl}
        z
    `;
    return (
        <svg width={width} height={height}>
            <path d={d} fill="black" />
        </svg>
    );
};

ReactDOM.render(
    <Rect width={200} height={100} tl={20} tr={0} br={20} bl={60} />,
    document.querySelector('#app'),
);