.slider {
    width: 100%;
    margin: 0 auto;
    /* add the following */
    display: flex;
    justify-content: center;
}

.slider div {
    margin-right: 28px;
}

.slider img {
    max-width: 100%;
    box-shadow: 2px 6px 8px 0 rgba(22, 22, 26, 0.18);
    border: none;
    border-radius: 10px;
    max-width: 100%;
    height: 100%;
}