loader.css

.preloader {
    background-color: #222222;
    position: fixed;
    left: 0;
    top: 0;
    height: 100%;
    width: 100%;
    z-index: 999999;
    display: flex;
    display: -ms-flexbox;
    -ms-flex-align: center;
    -ms-flex-pack: center;
    align-items: center;
    justify-content: center;
    transition: all 1s ease;
    -webkit-transition: all 1s ease;
}

.preloader.opacity-0 {
    opacity: 0;
}

.preloader .loader {
    height: 40px;
    width: 40px;
    border: 4px solid #e3e3e3;
    border-radius: 50%;
    border-top: 4px solid transparent;
    border-bottom: 4px solid transparent;
    animation: loader-spin 2s linear infinite;
    -webkit-animation: loader-spin 2s linear infinite;
}

@keyframes loader-spin {
    0% {
        transform: rotate(0deg);
        -webkit-transform: rotate(0deg);
    }

    100% {
        transform: rotate(360deg);
        -webkit-transform: rotate(360deg);
    }
}