accordion.css

.accordion {
    border: 1px solid hsl(0, 0%, 82%);
    border-radius: .3em;
    box-shadow: 0 1px 2px hsl(0, 0%, 82%);
}

.accordion > * + * {
    border-top: 1px solid hsl(0, 0%, 82%);
}

.accordion-control {
    color: hsl(0, 0%, 13%);
    display: block;
    font-size: 1rem;
    font-weight: normal;
    margin: 0;
    padding: 1em 1.5em;
    position: relative;
    width: 100%;
}

.accordion dt:first-child .accordion-control {
    border-radius: .3em .3em 0 0;
}

.accordion-control[aria-expanded="true"],
.accordion-control:focus,
.accordion-control:hover {
    background: hsl(0, 0%, 93%);
}

.accordion-control-icon {
    border: solid hsl(0, 0%, 62%);
    border-width: 0 2px 2px 0;
    height: .5rem;
    pointer-events: none;
    position: absolute;
    right: 1.5em;
    top: 50%;
    transform: translateY(-60%) rotate(45deg);
    width: .5rem;
}

.accordion-control:focus .accordion-control-icon,
.accordion-control:hover .accordion-control-icon {
    border-color: hsl(0, 0%, 13%);
}

.accordion-control[aria-expanded="true"] .accordion-control-icon {
    transform: translateY(-50%) rotate(-135deg);
}

.accordion-target {
    margin: 0;
    overflow: hidden;
    transition: cubic-bezier(.23, 1, .32, 1) .35s;
    transition-property: max-height, visibility;
    visibility: visible;
}

.accordion-target[aria-hidden="true"] {
    max-height: 0;
    visibility: hidden;
}

.accordion-target-inner {
    padding: 1em 1.5em;
}