If you want to prevent the so called FOUT or FOUC (Flash Of Unstyled Text or Content) and show a (fake) inline preloader bar until all resources are loaded.
Put the following code-snippets into your Webflow Custom Code Section (Page Settings)
Add this Custom Code inside <HEAD> tag:
Add this Custom Code before </BODY> tag:
Add the following two DIVs and class names inside Webflow
Make the outer DIV invisible (display: none)
Huge GIF image to simulate a heavy loading website