To switch the theme preloader you need to paste inside '.preloader-container' block. Here is the code for:
triangle preloader:
<svg id="Layer_1" x="0px" y="0px" width="150px" height="150px" viewBox="0 0 600 690" enable-background="new 0 0 600 690" xml:space="preserve"> <polygon fill="#FFFFFF" class="polygon" stroke="#A7A9AC" stroke-width="8" stroke-miterlimit="10" points="54.558,557.559 300,132.441 545.441,557.559 "/> <polygon fill="#8856A3" class="inner" points="96.037,535.115 300,168.885 503.963,535.115 "/> </svg>
color waves mask preloader:
<div class="color-wave"> <div class="img-box"> <canvas id="page-preloader"></canvas> <img src="images/t-shirt.png" alt=""> </div> </div>
For color waves preloader, change the image source to add your own image, the size of preloader will be the image natural size.