Default theme issue after upgrading 4.2.8 to 4.3.1

[Mariome]

Hi,

after upgrading from 4.2.8 to new version 4.3.1, I have problem with the default theme:

Menu navigator bar isn't working as you can see in the screen attached

https://i.imgur.com/Z2EKUYo.png

and as you can see "Indice, Contenuti non letti, Segna Tutto..." is in Italic mode, and all the site too.

Thank you