tabheader.css

div#ks-editor .tab-header {
    display: flex;
    margin-top: 0.2em;
    margin-bottom: 0.5em;
}

div#ks-editor .tab-button {
    display: block;

    font-size: medium;
    padding: 0.2em 0.5em;

    border-bottom: 1px solid gray;
    margin-bottom: 1px;

    margin-right: 0.2em;

    cursor: default;
}

div#ks-editor .tab-button:hover {
    margin-bottom: 0px;
    border-bottom: 2px solid gray;
}

div#ks-editor .tab-button.tab-open {
    font-weight: bold;
    margin-bottom: 0px;
    border-bottom: 2px solid black;
}