Team a dress shirt with a navy suit to be the definition of polish. If you need to instantly dial down your getup with one piece, enter black low top sneakers into the equation. That's the style for a guy in his 30s to convey he has what it takes to succeed.
A dress shirt and green chinos are appropriate for both semi-casual settings and day-to-day wear. Get a little creative in the shoe department and complement your outfit with a pair of black low top sneakers. Like this idea for your styling lineup as a 30-something gent?