Folyamatosan növekvő nyíl

.we-btn-expand {
    position: relative;

    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 14px;

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

    padding: 0 24px;

    border: 1px solid rgba(255,255,255,.14);
    border-radius: 10px;

    background: #10191c;
    color: #f2f4f0;

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

    cursor: pointer;
    overflow: hidden;

    transition:
        gap .5s cubic-bezier(.22,1,.36,1),
        border-radius .45s ease,
        border-color .4s ease,
        transform .4s ease,
        box-shadow .45s ease;
}

.we-btn-expand-text {
    position: relative;
    z-index: 2;

    transition:
        transform .5s cubic-bezier(.22,1,.36,1),
        color .35s ease;
}

.we-btn-expand-line {
    position: relative;
    z-index: 2;

    width: 0;
    height: 1px;

    background: #8ee8d4;

    transition:
        width .5s cubic-bezier(.22,1,.36,1);
}

.we-btn-expand-arrow {
    position: relative;
    z-index: 2;

    font-size: 20px;
    line-height: 1;

    transition:
        transform .55s cubic-bezier(.22,1,.36,1),
        color .35s ease;
}

.we-btn-expand:hover {
    gap: 9px;

    border-radius: 17px;
    border-color: rgba(142,232,212,.5);

    transform:
        translateY(-3px);

    box-shadow:
        0 18px 36px rgba(0,0,0,.38);
}

.we-btn-expand:hover .we-btn-expand-line {
    width: 28px;
}

.we-btn-expand:hover .we-btn-expand-text {
    transform:
        translateX(-3px);
}

.we-btn-expand:hover .we-btn-expand-arrow {
    transform:
        translateX(6px)
        scale(1.12);

    color: #8ee8d4;
}

.we-btn-expand:active {
    transform:
        translateY(0)
        scale(.97);
}

Ehhez az animációhoz nincs külön JavaScript.