  Kagome metals offer a unique platform for investigating robust
electron-correlation effects because of their lattice geometry, flat bands and
multi-orbital nature. In the cases with active flat bands, recent theoretical
studies have pointed to a rich phase diagram that contains not only electronic
orders but also quantum criticality. $\rm CsCr_3Sb_5$ has emerged as a strong
candidate for exploring such new physics. Here, using effective tight-binding
models obtained from ab initio calculations, we study the effects of electronic
correlations and symmetries on the electronic structure of $\rm CsCr_3 Sb_5$.
The effective tight-binding model and Fermi surface comprise multiple Cr-$d$
orbitals and Sb-$p$ orbitals. The introduction of Hubbard-Kanamori interactions
leads to orbital-selective band renormalization dominated by the $d_{xz}$ band,
concurrently producing emergent flat bands very close to the Fermi level. Our
analysis sets the stage for further investigations into the electronic
properties of $\rm CsCr_3Sb_5$, including electronic orders, quantum
criticality and unconventional superconductivity, which promise to shed much
new light into the electronic materials with frustrated lattices and bring
about new connections with the correlation physics of a variety of strongly
correlated systems.
