loader.html

<style>
        #loader {
            position: absolute;
            left: 50%;
            top: 50%;
            z-index: 1;
            margin: -75px 0 0 -75px;
            border: 16px solid rgba(209, 246, 254, 0.63);
            border-radius: 50%;
            border-top: 16px solid #3498db;
            width: 120px;
            height: 120px;
            -webkit-animation: spin 1s linear infinite;
            animation: spin 1s linear infinite;
        }

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

        @keyframes spin {
            0% {
                transform: rotate(0deg);
            }
            100% {
                transform: rotate(360deg);
            }
        }
</style>
<div id="loader"></div>