index.tsx

export interface ButtonProps extends ButtonHTMLAttributes<HTMLButtonElement> {
    primary?: boolean,
    accent?: boolean,
    additionalClass?: string,
}

...

const classNames = classnames(
        'btn',
        {
            primary
        },
        {
            accent
        },
        additionalClass
    );

...

<button className={classNames} {...props}>props.children</button>