Template for ?s= results?

Hello

I am developing a site on my localhost. My search results (for example: http://localhost/?s=books) are using search.php.

However if I search for http://localhost/?s= then the styling comes up really weird and it seems to be showing my standard recent posts loop but missing some important styling.

Does anybody know what template (not search.php) is called when you just use “http://localhost/?s=” ??

Thanks!