Branding overlapping navbar

Hi there,

Today I launched a new website of a client of mine, and I am currently experiencing a minor problem. It would be nice if you can check it out. The website is available here.

When I change the width of my browser screen to 991px, the navbar is overlapping the branding (boekhandelwever.nl). When reducing the width even more to 767px, the navbar is chaning into a dropdown menu.

I would love to have the same dropdown navbar toggled when the width of the screen is below 991px.

Can someone lead me through? I already experimented with the CSS @media but no results. I just got into bootstrap so I am not that experienced with that yet.

Thanks in advance.

Hindrik