From the Summary: "In the 117th Congress, Senate membership is evenly divided between the two political parties, with 50 Republicans, 48 Democrats, and 2 Independents who caucus with the Democrats. This is often referred to as a '50-50 Senate.' On February 3, 2021, the Senate approved S.Res. 27, a measure to provide the organizational basis for powersharing in the Senate when the parties are equally divided. Except for minor formatting changes, the resolution is identical to the one agreed to in 2001 when the Senate was most recently equally divided. The key provisions of the resolution are outlined [in the report]."
CRS Report for Congress, R46769
Congressional Research Service: https://crsreports.congress.gov/