The default style doesn't appear to be Core just as a heads up. Also... did you make a child style by chance? Ideally, you don't want to put edits in the main Core style, hence the name Core (DO NOT EDIT)
As for the logo, it looks like you may have set a 2x logo without it being 2x the size. Style properties -> Basic options, remove the 2x logo if it's the same image as the logo.
That's the correct method, sorry just wasn't sure because of the name. That bottom one is considered the child style. You can rename it whatever you want. The Core(main) should be left alone to preserve your changes on upgrades.