Best way to establish an application with a constant Header element(s), in which templates will be inserted below?

Something like this?

codepen

Note that in the real world, the sub-view templates would be separate .html files, as opposed to the embedded script tags you see in the codepen.

Yes seems perfect!
Thanks.
(will look at it more in detail afterward but looks like it is what I was trying to achieve)

I AGREE, FREAKING PERFECT!

Thank you VERY MUCH, sir.

Kind Regards,

-Jose.