Hello.
I had the same problem as described in http://support.themeburn.com/topic/checkout-and-login-buttons

@media (min-width: 769px) {
  .buttons [class*="left"] {
    order: 1;
    -ms-flex-pack: end;
    -webkit-justify-content: flex-end;
    justify-content: flex-end;
  }
  .buttons [class*="right"] {
    -ms-flex-pack: start;
    -webkit-justify-content: flex-start;
    justify-content: flex-start;
  }
}

I have updated custom CSS with code from the topic above.
It solved my problem on login page.
But at the same time I received another one: with position of buttons continue shopping and checkout on page checkout/cart.

Originally checkout button is on the right end and continue shopping on the left side.
But after applying code mentioned above button checkout become on the left side and button Continue shopping on the right side, which is not convenient.

Could you please help with this, but taking into account also login page and that script solved my first issue with buttons position on login page.

Thank you in advance.