21st Century Skills are Key to Individuals' Life-Long Success Act or the 21st Century SKILLS Act This bill establishes certain workforce innovation and opportunity accounts to provide employed or unemployed individuals and dislocated workers access to upskill training and other educational opportunities in order to meet 21st century workforce demands. Specifically, the bill (1) expands the use of certain workforce investment funds to provide workers with training and opportunities, and (2) replaces Technical Learning Accounts with Upskill Accounts to prepare employed or unemployed individuals for workforce demands. The Department of Labor must award grants to states to provide for subgrants to certain sector partnerships or labor-management partnerships. Priority must be given to sector partnerships or labor-management partnerships that (1) demonstrate they will prepare the local workforce for employment in growing in-demand industry sectors or occupations, and (2) target low-income individuals. In addition, Labor must also maintain a CareerOneStop website that contains, among other things (1) an Upskill Account Portal for eligible individuals to request such accounts, and (2) lists of approved training providers.