.install-btn {
    position: fixed;
    right: 18px;
    bottom: 18px;
    z-index: 30;
    min-height: 44px;
    border: 0;
    border-radius: 8px;
    background: #0F172A;
    color: #fff;
    padding: 10px 14px;
}
@media (max-width: 860px) {
    .install-btn { bottom: 144px; }
}