Searchform doesn't show properly in Safari, need CSS advices!

Hi everyone!

I’m having an issue with my searchform. I’m working with the great Pinboard Theme, and WordPress 4.4.2, and it’s the first time I’m trying to personnalize my website by using CSS. I know some basics about CSS but that’s all. I have a child theme.

I’m completely desperate and I hope someone will understand what’s wrong with my CSS. I have this searchform, that works perfectly fine on Chrome, Firefox, IE, Opera. But it doesn’t show properly on Safari (desktop) and also the android browser of my tablet. Chrome and firefox are ok on the tablet. When I’m using Safari, the searchform, which is supposed to be on the right side of the navigation, is shifting on the left. Moreover, I can see some text inside the “bubble” of the searchbar which is not supposed to be seen.

I learned that maybe the webkit-transition might not work properly, but even with this information there’s nothing I could do to make it work.

My website is https://www.zone-blanche.com.

Thank you and forgive me if it’s not crystal clear, since english is not my native language. I will provide more informations if you need it.