Seacrh.php changing format: adding horizontal box with test

I would like to add an horizontal box, with text inside in my search.php.
For example:
http://www.ricettedelcuore.it/?s=Polpo

I would like to add a Grey box, with written inside “basi”, before each post.
I would like a format very similar to
the one on the top of the page where it is written:
Home / Search results for “Polpo”

My problem is that i do not know how to write it.

Thank you
Chiara