.site-logo img { max-height: 200px; }

/* Center the container holding the logo */
.container-header .navbar-brand {
    float: none;
    text-align: center;
    width: 100%;
}

/* Center the image itself if it's treated as a block */
.container-header .navbar-brand img {
    margin: 0 auto;
    display: block;
}