:block(spin):mod(theme simple) {
    display: none;

    width: 20px;
    height: 20px;

    border: 2px dashed #000;
    border-radius: 50%;

    &:block(spin):mod(visible) {
        display: inline-block;

        animation: spin_theme_simple 2s infinite linear;
    }
}

@keyframes spin_theme_simple {
    from {
        transform: rotate(0);
    }
    to {
        transform: rotate(360deg);
    }
}