.pre-loader {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.pre-loader > .pre-loader-spinner {
    border: 4px solid #f3f3f3;
    border-radius: 50%;
    border-top: 4px solid #3498db;
    border-bottom: 4px solid #3498db;
    border-left: 4px solid #3498db;
    width: 64px;
    height: 64px;
    -webkit-animation: spin 1s linear infinite; /* Safari */
    animation: spin 1s linear infinite;
}

/* Safari */
@-webkit-keyframes spin {
    0% { -webkit-transform: rotate(0deg); }
    100% { -webkit-transform: rotate(360deg); }
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}