Wash strawberries and pat completely dry with paper towels; rest on a rack at room temperature for 10 minutes to remove any residual moisture.
Place chopped semi-sweet chocolate in a dry heatproof bowl and melt over simmering water (double boiler) stirring until smooth, or microwave in 20–30 second bursts at 50% power, stirring between bursts; remove from heat at 100–105°F and stir until glossy.
Stir in up to 1 tablespoon neutral oil or 1 tablespoon unsalted butter if needed to loosen chocolate for dipping; test with one strawberry for coating consistency.
Hold a strawberry by the stem, dip two-thirds into the melted chocolate, lift and allow excess to drip off, then place on a parchment-lined baking sheet; repeat with remaining berries, spacing them in a single layer.
Melt white chocolate similarly, transfer to a small piping bag, and drizzle over the dark-coated berries while shells are tacky; optionally sprinkle flaky sea salt immediately after drizzling.
Chill the sheet pan uncovered in the refrigerator for 10–15 minutes until the chocolate is firm to the touch, then transfer to a shallow container with parchment layers in between if storing; serve within 24–48 hours.
