Short-sleeve shirt: check. Sunscreen: check. Umbrella for surprise showers: check. It’s summertime and you know what that means: beer, strangers and pop-up parks. Downtown Denver’s Summer Mix, a series of programs set up by the Downtown Denver Partnership and Downtown Denver Business Improvement District, is back with some favorites, including the Skyline Beer Garden and Meet in the Street. The beer garden, at 16th and Arapahoe streets, will be open daily from June 9 through Oct.