hover.css

@import url('https://fonts.googleapis.com/css?family=Roboto&display=swap');
* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 10px;
    height: 100vh;
    display: flex;
    align-items: center;
    flex-direction: column;
    justify-content: center;
}

nav {
    display: inline-flex;
    flex-wrap: wrap;
    background: #fff;
    width: 100%;
    max-width: 631px;
    border: 3px solid #60D0E4;
    border-top-left-radius: 6px;
    border-bottom-left-radius: 6px;
    border-top-right-radius: 6px;
    border-bottom-right-radius: 6px;
    overflow: hidden;
}

nav a {
    display: block;
    padding: 20px 0;
    width: 125px;
    text-align: center;
    border-right: 3px solid #60D0E4;
    font-family: 'Roboto', sans-serif;
    color: #60D0E4;
    background: #fff;
}

nav a:last-child {
    border-right: 0;
}

nav a:hover {
    color: #fff;
    background: #60D0E4;
    font-weight: bold;
    animation: growShrink 1s linear forwards;
}

@keyframes growShrink {
    0% {
        letter-spacing: 0;
    }
    16% {
        letter-spacing: 2px;
    }
    33% {
        letter-spacing: 0;
    }
    50% {
        letter-spacing: 1px;
    }
    70% {
        letter-spacing: 0;
    }
    100% {
        letter-spacing: 2px;
    }
}