Try going to your game.prefs (there's a button leading to it in the top left of the client) and setting the ui_scale to 1 to fix the UI scaling outside the window. I play on windows so I'm not sure why your game has no borders, but the window size options are also in the prefs file under Windows in Main. There is also an option primary_adapter in the same place as ui_scale, and you can set it as primary_adapter = 'windowed',. Windowed is recommended for the game as it is old and breaks with alt-tab.

Ah the time tested Blodir answer of attack when your opponent eco's, defend when your opponent attacks and eco when your opponent defends.