Hi. It is totally what I need. How can I set up for images on the loading like background images, logo?
Viewing post in (Unity) Better Minimal WebGL Template comments
The default template included in Unity (the non-minimal one) includes a loading bar. I'd recommend taking a look at the source for that and copying over the bits you'd like to use.
If you just want a static loading image, you can add an extra line of CSS to give the game a background while it's loading.