.c5-example summary {
    list-style: none;
    margin-bottom: .75em;
}

.c5-example summary::before {
    content: '';
    display: inline-block;
    margin-bottom: -.75em;
    height: 2.5em;
    width: 2.5em;
    background-image: url('https://files.instruct.nl/fundament/C_Informatie/interactief/c5/idea.png');
    background-repeat: no-repeat;
    background-position: center;
    background-size: contain;
}
.c5-example[open] summary::before, .c5-example summary:hover::before {
    background-image: url('https://files.instruct.nl/fundament/C_Informatie/interactief/c5/idea_glow.png');
}

.darkmode .c5-example summary::before {
    background-image: url('https://files.instruct.nl/fundament/C_Informatie/interactief/c5/idea_dark.png');
}

.darkmode .c5-example[open] summary::before, .darkmode .c5-example summary:hover::before {
    background-image: url('https://files.instruct.nl/fundament/C_Informatie/interactief/c5/idea_glow_dark.png');
}