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

summary::after {
    content: '►';
    background: none;
    border-color: #3d6f96;
    color: #3d6f96;
    font-size: 16px;
    border: 2px solid;
    line-height: 1;
    text-align: center;
    text-decoration: none;
    transition: 0.25s;
    border-radius: 10px;
    cursor: pointer;
    -webkit-touch-callout: none; /* iOS Safari */
    -webkit-user-select: none; /* Safari */
    -khtml-user-select: none; /* Konqueror HTML */
    -moz-user-select: none; /* Old versions of Firefox */
    -ms-user-select: none; /* Internet Explorer/Edge */
    user-select: none; /* Non-prefixed version, currently*/
    padding: 1px 4px;
    margin: 4px 4px;
}

details:hover summary:after  {
    background-color: #3d6f96;
    text-decoration: none;
    cursor: pointer;
    border-color: #3d6f96;
    color: #FFFFFF;
}

details[open] summary:after {
    content: "▼";
}