Button styling is available as a setting on the user's Preferences page. There are different spacing options available, and the spacing option persists across all boards, there is no per-board spacing option in CoughDrop. Button spacing is a per-device setting, allowing you to change the spacing depending on the size of the device (a mobile phone, for example, might require less spacing between buttons).
Access to the Preferences page by hitting the profile icon in the top right corner and selecting "Preferences".
Button Spacing option
Select the button spacing option you prefer for the current device. Then hit "Save Preferences" to record your changes.