body {
	width: 35em;
	margin: 0 auto;
	font-family: Tahoma, Verdana, Arial, sans-serif;
}
details > summary {
    list-style-type: none;
}

details > summary::-webkit-details-marker {
    display: none;
}

details > summary::before {
    content: '⬡  ';
}

details[open] > summary::before {
    content: '⬢  ';
}

details {
    border: 0px solid gray;
    border-radius: 0.2rem;
    padding: 0.5rem;
}

details[open] > summary {
    margin-bottom: 0.5rem;
}