Kettéhasadó zöld felület

.we-btn-open {
    position: relative;

    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 16px;

    min-width: 175px;
    height: 54px;

    padding: 0 26px;

    border: 1px solid rgba(63,159,99,.35);
    border-radius: 12px;

    background: #101713;
    color: #f1f3ee;

    font-family: Arial, sans-serif;
    font-size: 14px;
    font-weight: 500;
    letter-spacing: .4px;

    cursor: pointer;
    overflow: hidden;

    transition:
        transform .7s cubic-bezier(.22,1,.36,1),
        border-radius .7s ease,
        box-shadow .7s ease;
}

.we-btn-open-left,
.we-btn-open-right {
    position: absolute;

    top: 0;

    width: 50%;
    height: 100%;

    background: #3f9f63;

    transition:
        transform 1s cubic-bezier(.22,1,.36,1);
}

.we-btn-open-left {
    left: 0;
    transform-origin: left center;
}

.we-btn-open-right {
    right: 0;
    transform-origin: right center;
}

.we-btn-open-text,
.we-btn-open-arrow {
    position: relative;
    z-index: 2;

    transition:
        transform .8s cubic-bezier(.22,1,.36,1),
        color .6s ease;
}

.we-btn-open-arrow {
    font-size: 20px;
}

.we-btn-open:hover {
    transform:
        translateY(-4px);

    border-radius: 18px;

    box-shadow:
        0 20px 42px rgba(0,0,0,.42);
}

.we-btn-open:hover .we-btn-open-left {
    transform:
        translateX(-102%);
}

.we-btn-open:hover .we-btn-open-right {
    transform:
        translateX(102%);
}

.we-btn-open:hover .we-btn-open-text {
    transform:
        translateX(-4px);

    color: #8ac99b;
}

.we-btn-open:hover .we-btn-open-arrow {
    transform:
        translateX(8px)
        scale(1.12);

    color: #5fbd7d;
}

.we-btn-open:active {
    transform:
        translateY(-1px)
        scale(.97);
}

Ehhez az animációhoz nincs külön JavaScript.