harmonious

Harmonious means fitting together pleasantly, whether in sound or in dealings between people. Nothing clashing.

Music has the literal sense, where harmonious notes sound well together. The commoner use is about relationships, so a harmonious workplace and harmonious relations between neighbours are both free of friction. Design borrows it for colour and proportion. The noun harmony covers all of it, and living in harmony is the fixed phrase. Its opposite in music is discordant, and in human terms it is simply fractious.