Mantra theme problems

Hello,

For the past few hours I’ve been streaching my head, trying to customize Mantra theme. The problem I ran in-to is about header banner area and top menus. I wanted my top banner to be behing the menu tabs , but my menu tabs seem to be separated from the banner image wtih a grey stripe in between. I figured that maybe it had something to do with the color of menus , so I made it transparent and so I messed it up . Now the round cornered menu tabs are gone , all I have is a Home tab that seems to be more on the page than header.

Sorry for my english. Here’s my site , maybe you’ll get what im saying when you see it https://www.trippinsociety.com

How do I make tabs appear over the header picture ?