1. Combine sugar and 1/3 cup water in a small saucepan and bring to a boil over high heat, stirring occasionally. Reduce heat to medium-low and simmer until sugar has dissolved, about 3 minutes. Remove from heat and let cool. Stir in lime zest and juice; let cool to room temperature.
2. Mix strawberries with mangoes in a large bowl. Add syrup and gently stir until well mixed. Refrigerate at least 30 minutes or until ready to serve.