<button class="button">Button</button>
<button class="button alternative">Playful hover!</button>
<button class="button simple">Simple</button>

<!-- dribbble - twitter -->
<a class="dribbble" href="https://dribbble.com/shots/9733513-Playful-button-hovers" target="_blank"><img src="https://cdn.dribbble.com/assets/dribbble-ball-mark-2bd45f09c2fb58dbbfb44766d5d1d07c5a12972d602ef8b32204d28fa3dda554.svg" alt=""></a>
<a class="twitter" target="_blank" href="https://twitter.com/aaroniker_me"><svg xmlns="http://www.w3.org/2000/svg" width="72" height="72" viewBox="0 0 72 72"><path d="M67.812 16.141a26.246 26.246 0 0 1-7.519 2.06 13.134 13.134 0 0 0 5.756-7.244 26.127 26.127 0 0 1-8.313 3.176A13.075 13.075 0 0 0 48.182 10c-7.229 0-13.092 5.861-13.092 13.093 0 1.026.118 2.021.338 2.981-10.885-.548-20.528-5.757-26.987-13.679a13.048 13.048 0 0 0-1.771 6.581c0 4.542 2.312 8.551 5.824 10.898a13.048 13.048 0 0 1-5.93-1.638c-.002.055-.002.11-.002.162 0 6.345 4.513 11.638 10.504 12.84a13.177 13.177 0 0 1-3.449.457c-.846 0-1.667-.078-2.465-.231 1.667 5.2 6.499 8.986 12.23 9.09a26.276 26.276 0 0 1-16.26 5.606A26.21 26.21 0 0 1 4 55.976a37.036 37.036 0 0 0 20.067 5.882c24.083 0 37.251-19.949 37.251-37.249 0-.566-.014-1.134-.039-1.694a26.597 26.597 0 0 0 6.533-6.774z"></path></svg></a>
.button {
    &.alternative {
        --color-hover: #2B3044;
        --background: #362A89;
        --hover-back: #6D58FF;
        --hover-front: #F6F8FF;
    }
    &.simple {
        --background: #275EFE;
        --background-hover: #1749DB;
    }
}

.button {
    --color: #fff;
    --color-hover: var(--color);
    --background: #2B3044;
    --background-hover: var(--background);
    --hover-back: #6D58FF;
    --hover-front: #5C86FF;
    padding: 8px 28px;
    border-radius: 20px;
    line-height: 24px;
    font-size: 14px;
    font-weight: 600;
    letter-spacing: .02em;
    border: none;
    outline: none;
    position: relative;
    overflow: hidden;
    cursor: pointer;
    -webkit-appearance: none;
    -webkit-tap-highlight-color: transparent;
    -webkit-mask-image: -webkit-radial-gradient(white, black);
    color: var(--c, var(--color));
    background: var(--b, var(--background));
    transition: color .2s linear var(--c-d, .2s), background .3s linear var(--b-d, .2s);
    &:not(.simple) {
        &:before,
        &:after {
            content: '';
            position: absolute;
            background: var(--pb, var(--hover-back));
            top: 0;
            left: 0;
            right: 0;
            height: 200%;
            border-radius: var(--br, 40%);
            transform: translateY(var(--y, 50%));
            transition: transform var(--d, .4s) ease-in var(--d-d, 0s), border-radius .5s ease var(--br-d, .08s);

        }
        &:after {
            --pb: var(--hover-front);
            --d: .44s;
        }
    }
    div {
        z-index: 1;
        position: relative;
        display: flex;
        span {
            display: block;
            backface-visibility: hidden;
            transform: translateZ(0);
            animation: var(--name, none) .7s linear forwards .18s;
        }
    }
    &.in {
        --name: move;
        &:not(.out) {
            --c: var(--color-hover);
            --b: var(--background-hover);
            &:before,
            &:after {
                --y: 0;
                --br: 5%;
            }
            &:after {
                --br: 10%;
                --d-d: .02s;
            }
        }
        &.out {
            --name: move-out;
            &:before {
                --d-d: .06s;
            }
        }
    }
}

@keyframes move {
    30%,
    36% {
        transform: translateY(calc(-6px * var(--move))) translateZ(0) rotate(calc(-13deg * var(--rotate) * var(--part)));
    }
    50% {
        transform: translateY(calc(3px * var(--move))) translateZ(0) rotate(calc(6deg * var(--rotate) * var(--part)));
    }
    70% {
        transform: translateY(calc(-2px * var(--move))) translateZ(0) rotate(calc(-3deg * var(--rotate) * var(--part)));
    }
}

@keyframes move-out {
    30%,
    36% {
        transform: translateY(calc(6px * var(--move))) translateZ(0) rotate(calc(13deg * var(--rotate) * var(--part)));
    }
    50% {
        transform: translateY(calc(-3px * var(--move))) translateZ(0) rotate(calc(-6deg * var(--rotate) * var(--part)));
    }
    70% {
        transform: translateY(calc(2px * var(--move))) translateZ(0) rotate(calc(3deg * var(--rotate) * var(--part)));
    }
}

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

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

// Center & dribbble
body {
    min-height: 100vh;
    display: flex;
    font-family: 'Inter UI', 'Inter', Arial;
    justify-content: center;
    align-items: center;
    background: #E1E6F9;
    @media(max-width: 440px) {
        flex-direction: column;
    }
    .button {
        display: block;
        margin: 0 8px;
        &:first-child {
            margin-left: 0;
        }
        &:last-child {
            margin-right: 0;
        }
        @media(max-width: 440px) {
            margin: 8px 0;
        }
    }
    .dribbble {
        position: fixed;
        display: block;
        right: 20px;
        bottom: 20px;
        img {
            display: block;
            height: 28px;
        }
    }
    .twitter {
        position: fixed;
        display: block;
        right: 64px;
        bottom: 14px;
        svg {
            width: 32px;
            height: 32px;
            fill: #1da1f2;
        }
    }
}
View Compiled
document.querySelectorAll('.button').forEach(button => {

    let div = document.createElement('div'),
        letters = button.textContent.trim().split('');

    function elements(letter, index, array) {

        let element = document.createElement('span'),
            part = (index >= array.length / 2) ? -1 : 1,
            position = (index >= array.length / 2) ? array.length / 2 - index + (array.length / 2 - 1) : index,
            move = position / (array.length / 2),
            rotate = 1 - move;

        element.innerHTML = !letter.trim() ? '&nbsp;' : letter;
        element.style.setProperty('--move', move);
        element.style.setProperty('--rotate', rotate);
        element.style.setProperty('--part', part);

        div.appendChild(element);

    }

    letters.forEach(elements);

    button.innerHTML = div.outerHTML;

    button.addEventListener('mouseenter', e => {
        if(!button.classList.contains('out')) {
            button.classList.add('in');
        }
    });

    button.addEventListener('mouseleave', e => {
        if(button.classList.contains('in')) {
            button.classList.add('out');
            setTimeout(() => button.classList.remove('in', 'out'), 950);
        }
    });

});
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