Y. Warlinda, K. A. Muhammad Saeed Aledresi, S. Halbi, and C. Putri, “Content Learning System (CLS) Validity and Practicality in Atomic Theory on Project Based Learning (PjBL) with Flipped Classroom For Senior High School In Indonesia”, JHICE, vol. 1, no. 01, pp. 12-23, Jun. 2021.