Newbie Help

I need some help with my website. I am a complete newbie when it comes to CSS and cannot for the life of me figure out how to make things work

For starters my website is bearlypaperco.com
1. I would like to take that navigation menu and move it right under the header, centered. I would like the push the header up a bit so there isn’t so much white space.
2. when you click on “Add to cart” button, another button pops up underneath but it looks different. I would like them to both look the same but have no idea where to look to fix this
3. my biggest issue, when trying to view my website on mobile, it goes to my blog page first. You have to click on the menu and make it redirect to the website that way. I would like the blog page to not even show up, just have that home page open up right away.

Any help you can provide would be amazing!
Thank you!!

The page I need help with: [log in to see the link]