JS code ?
Where is javascript code for navbar ,Modals,....,. ?
Nowhere? To quote the documentation:
Spectre.css does not include JavaScript code, you will need to implement your JS to interact with modals.
# but why navbar is not responsive

Haven't used the navbar and I'm not the author of Spectre.css, but responsiveness doesn't require JS. You might want to report this issue as a bug.
You'd have to write your own JS to change the display of the navbar. In to a burger menu for example. If you want a out the box responsive menu use tabs
@9Emi There is no JS in Spectre, because JS code is opinionated thing. There are already some pure CSS solutions.
Why not leave this half-done? Why not make it working out of box with CSS built in spectre? This tab-thing is very useful. Please consider implementing it out of box.
Which Spectre components require JS? Modals, accordions and tabs are pure CSS, no JS in my version 0.6.0.