I am not much of a technical/dev guy so apologies for the question if it's something obvious, but:
In Visual Studio, where I write my index.html. what I see at the top is this:
<!DOCTYPE html>
<html class="no-js">
<head>
<!-- Google Tag Manage
HOWEVER - when I run F12 on the site it self - I get this:

And ONLY then the <!DOCTYPE html>.....
Is this ok?
Thanks
Looks fine to me.
The dev tools shows how the page is rendered