When you start a game session on Boosteroid and see a black border around the game image, more likely, your screen resolution is above 1920x1080. Take a look at the screenshot.
You may try to zoom the page to get rid of black bars. To do this, you need to press Ctrl (Windows) or Command (Mac) and turn the mouse wheel up or press 3 dots in the upper-right corner of the browser:
Keep in mind that we support only the following screen resolutions: