<div class="menu">
    <label for="menu_bar01">アコーディオン１</label>
    <input type="checkbox" id="menu_bar01" />
    <ul id="links01">
        <li><a href="">Link01</a></li>
        <li><a href="">Link02</a></li>
        <li><a href="">Link03</a></li>
        <li><a href="">Link04</a></li>
    </ul>
    <label for="menu_bar02">アコーディオン２</label>
    <input type="checkbox" id="menu_bar02" />
    <ul id="links02">
        <li><a href="">Link01</a></li>
        <li><a href="">Link02</a></li>
        <li><a href="">Link03</a></li>
        <li><a href="">Link04</a></li>
    </ul>
</div>
.menu {
    max-width: 600px;
}

.menu a {
    display: block;
    padding: 15px;
    text-decoration: none;
    color: #000;
}

label {
    display: block;
    margin: 0 0 4px 0;
    padding : 15px;
    line-height: 1;
    color :#fff;
    background : green;
    cursor :pointer;
}

input {
    display: none;
}

.menu ul {
    margin: 0;
    padding: 0;
    background :#f4f4f4;
    list-style: none;
}

.menu li {
    height: 0;
    overflow: hidden;
    -webkit-transition: all 0.5s;
    -moz-transition: all 0.5s;
    -ms-transition: all 0.5s;
    -o-transition: all 0.5s;
    transition: all 0.5s;
}

#menu_bar01:checked ~ #links01 li,
#menu_bar02:checked ~ #links02 li {
    height: 54px;
    opacity: 1;
}

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