Position buttons for mobile

Hello :)

I need help with positioning my buttons. Ideal would be: the first button centered on the screen and the following two buttons on the left side, alligning to the textblocks. 

So far i used this Code to resize the buttons: 

@media screen and (max-width:767px) {
div#block-f2a8291c0bdfb307573a a {
    font-size: 14px !important; width : 200px;
}
}

and with this one i tried to center them: 

@media screen and (max-width:767px) {
div#block-f2a8291c0bdfb307573 a
{ display: flex;
  justify-content: center;
  align-items: center;
}
}

Since i only have 3 Buttons on my page i went with the block-codes. But i guess the problem is with that frame that comes from squarespace (see picture). Maybe if i can center my buttons inside that frame it would work somehow. 

The URL is: https://amethyst-pelican-2l2k.squarespace.com/
The password is: umowebseite

Thank You!