focalboard/website/site/static/css/tabs.css

div.tab {
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
}

div.tab button {
    background-color: inherit;
    float: left;
    border: none;
    outline: none;
    cursor: pointer;
    padding: 14px 16px;
    transition: 0.3s;
}

div.tab button:hover {
    background-color: #ddd;
}

div.tab button.active {
    background-color: #ccc;
}

.tabcontent {
    display: none;
    padding: 25px 12px;
    border: 1px solid #ccc;
    border-top: none;
}

.tabcontent {
    -webkit-animation: fadeEffect 1s;
    animation: fadeEffect 1s; /* Fading effect takes 1 second */
}

@-webkit-keyframes fadeEffect {
    from {opacity: 0;}
    to {opacity: 1;}
}

@keyframes fadeEffect {
    from {opacity: 0;}
    to {opacity: 1;}
}