html,
body {
    background: rgb(73,148,226);
    background: linear-gradient(180deg, rgba(73,148,226,1) 0%, rgba(73,148,226,0.2) 50%, rgba(255,255,255,1) 100%);
}

html {
    height: 100%;
}

body {
    min-height: 100%;
}

.logo-container {
    height: 100%;      /* Equals maximum image height */
    width: 100%;
    white-space: nowrap; /* This is required unless you put the helper span closely near the img */
    text-align: center;
    margin: 0;
}

.helper {
    display: inline-block;
    height: 80%;
    vertical-align: middle;
}

.logo {
    max-width: 18%;
    height: auto;
    vertical-align: middle;
}