:root {
    color-scheme: only light;
}

#stim1 {
    width: 15vw;
    height: 15vw;
    background: orange;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%);
}

#stim2 {
    width: 15vw;
    height: 15vw;
    background: DodgerBlue;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%);
}

#stim1-responded {
    width: 15vw;
    height: 15vw;
    background: orange;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%);
    -moz-box-shadow: inset 0 0 40px #000000;
    -webkit-box-shadow: inset 0 0 40px #000000;
    box-shadow: inset 0 0 40px #000000;
}

#stim2-responded {
    width: 15vw;
    height: 15vw;
    background: DodgerBlue;
    position: absolute;
    top: 50%;
    left: 50%;
    margin-right: -50%;
    transform: translate(-50%, -50%);
    -moz-box-shadow: inset 0 0 40px #000000;
    -webkit-box-shadow: inset 0 0 40px #000000;
    box-shadow: inset 0 0 40px #000000;
}