.collapsible_panel {
    background-color: #777;
    color: white;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
    margin-top:10px;
}

    .active, .collapsible_panel:hover {
        background-color: #555;
    }

    .collapsible_panel:after {
        content: '\2212';
        color: white;
        font-weight: bold;
        float: right;
        margin-left: 5px;
    }

.active:after {
    content: "\002B";
}

.collapsible_panel_content {
    padding: 0 18px;
    max-height: 100%;
    overflow: hidden;
    transition: max-height 0.2s ease-out;
    background-color: #f1f1f1;
    display: block;
}