Complex sentence: String instrument design was refined during the Renaissance and into the Baroque period (1600-1750) of musical history--violins and guitars became more stable in terms of their design changes, and were roughly similar to what we use in the 2000s.
Split into simpler sentences: String instrument design refined during the Renaissance and into the Baroque period (1600-1750) of musical history. Violins and guitars became more consistent in design, and were roughly similar to what we use in the 2000s.