If you look at -> http://akveo.com/ngx-admin/ , you can see the effect you're looking for.
The way they achieved it is by putting the code bellow <my-app> Loading... </myapp> in the index.html file.
Here is the link to their repo -> https://github.com/akveo/ngx-admin, and the body part of index.html you're looking for looks like:
<body>
<ngx-app>Loading...</ngx-app>
<style>@-webkit-keyframes spin{0%{transform:rotate(0)}100%{transform:rotate(360deg)}}@-moz-keyframes spin{0%{-moz-transform:rotate(0)}100%{-moz-transform:rotate(360deg)}}@keyframes spin{0%{transform:rotate(0)}100%{transform:rotate(360deg)}}.spinner{position:fixed;top:0;left:0;width:100%;height:100%;z-index:1003;background: #000000;overflow:hidden} .spinner div:first-child{display:block;position:relative;left:50%;top:50%;width:150px;height:150px;margin:-75px 0 0 -75px;border-radius:50%;box-shadow:0 3px 3px 0 rgba(255,56,106,1);transform:translate3d(0,0,0);animation:spin 2s linear infinite} .spinner div:first-child:after,.spinner div:first-child:before{content:'';position:absolute;border-radius:50%} .spinner div:first-child:before{top:5px;left:5px;right:5px;bottom:5px;box-shadow:0 3px 3px 0 rgb(255, 228, 32);-webkit-animation:spin 3s linear infinite;animation:spin 3s linear infinite} .spinner div:first-child:after{top:15px;left:15px;right:15px;bottom:15px;box-shadow:0 3px 3px 0 rgba(61, 175, 255,1);animation:spin 1.5s linear infinite}</style>
<div id="nb-global-spinner" class="spinner">
<div class="blob blob-0"></div>
<div class="blob blob-1"></div>
<div class="blob blob-2"></div>
<div class="blob blob-3"></div>
<div class="blob blob-4"></div>
<div class="blob blob-5"></div>
</div>
</body>