- var entries = [['calendar', 'Events'], ['files', 'Files'], ['notification', 'Notification'], ['settings', 'Settings']];

nav(class='tabbar')
  ul
    each entry, i in entries
      - var cls = ''
      - if(i == 0)
        - cls = 'active'
      li(class=cls + ' ' + entry[0])
        a(href='')
          div
          span=entry[1]

a(class='dribbble' href='https://dribbble.com/shots/7164420-Liquid-tab-bar-animation' target='_blank')
  img(src='https://cdn.dribbble.com/assets/dribbble-ball-mark-2bd45f09c2fb58dbbfb44766d5d1d07c5a12972d602ef8b32204d28fa3dda554.svg')
View Compiled
.tabbar {
    --primary: #275EFE;
    --background: #fff;
    --inactive: #99A3BA;
    --shadow: rgba(18, 22, 33, .24);
    --line: #CDD9ED;
    background: var(--background);
    box-shadow: 0 1px 4px -1px var(--shadow);
    border-radius: 5px 5px 21px 21px;
    width: 360px;
    -webkit-tap-highlight-color: transparent;
    overflow: hidden;
    ul {
        --x: 54px;
        margin: 0;
        padding: 0 12px;
        list-style: none;
        display: grid;
        position: relative;
        overflow: hidden;
        text-align: center;
        grid-template-columns: repeat(4, minmax(0, 1fr));
        &:before {
            content: '';
            position: absolute;
            top: 0;
            left: var(--x);
            background: var(--primary);
            width: 60px;
            margin-left: -30px;
            height: 40px;
        }
        li {
            position: relative;
            &:before,
            &:after {
                content: '';
                background: var(--background);
                height: 44px;
                width: 84px;
                position: absolute;
                top: 0;
                left: 50%;
                margin-left: -42px;
            }
            &:before {
                border-radius: 0 48% 0 0;
            }
            &:after {
                border-radius: 48% 0 0 0;
            }
            a {
                padding: 20px 0;
                display: block;
                text-decoration: none;
                position: relative;
                z-index: 1;
                color: var(--primary);
                transition: transform .2s ease;
                &:active {
                    transform: scale(.9);
                }
                &:before,
                &:after {
                    content: '';
                    top: 0;
                    left: 50%;
                    position: absolute;
                    background: var(--primary);
                    border-radius: 1px;
                    width: 2px;
                    margin-left: -1px;
                    transform-origin: 50% 0;
                    transform: translateY(-14px) scaleX(.6);
                }
                &:before {
                    height: 8px;
                }
                &:after {
                    height: 4px;
                }
                div {
                    background: var(--inactive);
                    width: 24px;
                    height: 24px;
                    margin: 0 auto 4px auto;
                    &:before {
                        --y: -100%;
                        content: '';
                        display: block;
                        width: 100%;
                        height: 100%;
                        top: 0;
                        left: 0;
                        transform: translateY(var(--y));
                        position: absolute;
                        transition: transform .4s linear;
                        background: var(--primary);
                    }
                }
                span {
                    display: block;
                    font-weight: 500;
                    font-size: 14px;
                    opacity: 0;
                    transition: opacity .36s linear;
                }
            }
            &.active {
                &:before {
                    animation: before 1.1s ease;
                }
                &:after {
                    animation: after 1.1s ease;
                }
                a {
                    animation: bounce .9s linear .3s;
                    &:before {
                        animation: drop .4s linear .1s forwards;
                    }
                    &:after {
                        animation: drop .5s linear .13s forwards;
                    }
                    div {
                        &:before {
                            --y: 0;
                            transition-delay: .3s;
                        }
                    }
                    span {
                        opacity: 1;
                        transition-delay: .38s;
                    }
                }
            }
            &.calendar {
                a {
                    div {
                        -webkit-mask-box-image: url('https://aaroniker.me/feather-icons/calendar.svg');
                        mask: url('https://aaroniker.me/feather-icons/calendar.svg');
                    }
                }
            }
            &.files {
                a {
                    div {
                        -webkit-mask-box-image: url('https://aaroniker.me/feather-icons/file.svg');
                        mask: url('https://aaroniker.me/feather-icons/file.svg');
                    }
                }
            }
            &.notification {
                a {
                    div {
                        -webkit-mask-box-image: url('https://aaroniker.me/feather-icons/bell.svg');
                        mask: url('https://aaroniker.me/feather-icons/bell.svg');
                    }
                }
            }
            &.settings {
                a {
                    div {
                        -webkit-mask-box-image: url('https://aaroniker.me/feather-icons/settings.svg');
                        mask: url('https://aaroniker.me/feather-icons/settings.svg');
                    }
                }
            }
        }
    }
}

@keyframes bounce {
    40% {
        transform: translateY(9px);
    }
    55% {
        transform: translateY(-1px);
    }
    70% {
        transform: translateY(4px);
    }
}

@keyframes drop {
    50% {
        transform: translateY(10px) scaleY(1.2) scaleX(.5);
    }
    100% {
        transform: translateY(20px) scaleY(0) scaleX(.5);
    }
}

@keyframes before {
    45%,
    55% {
        transform: translateX(-41px);
    }
}

@keyframes after {
    45%,
    55% {
        transform: translateX(41px);
    }
}

html {
    box-sizing: border-box;
    -webkit-font-smoothing: antialiased;
}

* {
    box-sizing: inherit;
    &:before,
    &:after {
        box-sizing: inherit;
    }
}

// Center & dribbble
body {
    font-family: 'Roboto', Arial;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: #EEF4FF;
    .dribbble {
        position: fixed;
        display: block;
        right: 20px;
        bottom: 20px;
        img {
            display: block;
            height: 28px;
        }
    }
}
View Compiled
$('.tabbar ul li a').click(function(e) {

    let link = $(this),
        li = link.parent();

    setActive(li.parent(), li);

    return false;

});

function setActive(nav, li) {
    nav.find('li').removeClass('active');
    li.addClass('active');
    nav.css('--x', li.position().left + li.outerWidth() / 2 + 'px');
}

External CSS

  1. https://fonts.googleapis.com/css?family=Roboto:400,500,700&display=swap

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js