Add a placeholder to the examples

[gero3]

Related issue: Fixed #19786.

Description

This adds a placeholder.html in the viewer when there is no example selected. This placeholder tells the viewers to select an example.

https://raw.githack.com/gero3/three.js/AddPlaceholder/examples/index.html

[gero3]

Is there any interest in this?

[Mugen87]

I would style the text a bit more subtle by removing the dark background box and make the text color light gray. Right now, I have the feeling the new section draws too much attention on it.

[WestLangley]

nit: maybe this text, instead

Select an example from the sidebar.

[gero3]

I've updated this branch.

[mrdoob]

This is definitely interesting!
But I don't think we need another html file for this... Shouldn't it be possible to do it inside index.html?
That way we don't need to modify e2e.

[gero3]

@mrdoob

The PR has been updated to make it contained in index.html

[mrdoob]

Nice! I didn't know about <template> 🤓

[gero3]

I've updated the template.

The result didn't change =>

Nice! I didn't know about <template> 🤓

Yes, It is a good way to hide HTML inside HTML without it rendering. It also makes it easy to view in the IDE because it detects it as HTML.

[mrdoob]

Thanks!