How to conditionally apply css in emotion js

Issue #649

Check flag then define css

const Picture = (feature) => {
    const shadowCss = feature.shadow ? css`
        border-radius: 5px;
        box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2), 0 6px 20px 0 rgba(0, 0, 0, 0.19);
    ` : css``

    return (
        <div css={css`
            width: 40vw;
            @media (max-width: 420px) {
                width: 98vw;
            }
        `}>
            <div css={shadowCss}>
                <img css={css`
                max-width: 100%;
                height: auto;
            `}
                    src={require(`../apps/${feature.image}`)}
                />
            </div>
        </div>
    )
}