.content {
    padding: .5rem 1rem 2rem;
}

.elem_hide {
    opacity: 50%;
}

#footer {
    height: 100px;
    background-color: aliceblue;
}

.expander {
    display: none;
}

.expander+label {
    margin-bottom: 0 !important;
}

input+label::before {
    content: '\2B9E';
}

input:checked+label::before {
    content: '\2B9F';
}

input ~ ul {
    display: none;
}

input:checked ~ul {
    display: block;
}