  The entanglement of charge density wave (CDW), superconductivity, and
topologically nontrivial electronic structure has recently been discovered in
the kagome metal $A$V$_3$Sb$_5$ ($A$ = K, Rb, Cs) family. With high-resolution
angle-resolved photoemission spectroscopy, we study the electronic properties
of CDW and superconductivity in CsV$_3$Sb$_5$. The spectra around $\bar{K}$ is
found to exhibit a peak-dip-hump structure associated with two separate
branches of dispersion, demonstrating the isotropic CDW gap opening below
$E_{\rm F}$. The peak-dip-hump lineshape is contributed by linearly dispersive
Dirac bands in the lower branch and a dispersionless flat band close to $E_{\rm
F}$ in the upper branch. The electronic instability via Fermi surface nesting
could play a role in determining these CDW-related features. The
superconducting gap of $\sim$0.4 meV is observed on both the electron band
around $\bar{\Gamma}$ and the flat band around $\bar{K}$, implying the
multiband superconductivity. The finite density of states (DOS) at $E_{\rm F}$
in the CDW phase are most likely in favor of the emergence of multiband
superconductivity, particularly the enhanced DOS associated with the flat band.
Our results not only shed light on the controversial origin of the CDW, but
also offer insights into the relationship between CDW and superconductivity.
