[Theme: Colinear] Can I make the logo bigger? ( 2 more questions)

I’m going to be buying my domain today, and then I’ll start using it with www.remarpro.com, but for now I’m only playing around with the Colinear theme on wordpress.com. I assume it works the same, so I have a few questions:

1. Can I make the logo at the very top (not the header image) bigger, e.g. so that it spans the entire page rather than just occupying a portion of it?

2. When I use the black background color scheme, the dropdown menu for categories has a glitch. All choices, except for the one you’re hovering over, are white and thus invisible. Can this be fixed, so that the choices are visible like they are with a different color scheme?

3. Can I give the readers a choice between the black and white color schemes within this same theme? If so, how?