  Temperature-dependent reflectivity measurements on the kagome metal
CsV$_3$Sb$_5$ in a broad frequency range of $50-20000$~cm$^{-1}$ down to
$T$=10~K are reported. The charge-density wave (CDW) formed below $T_{\rm CDW}$
= 94~K manifests itself in a prominent spectral-weight transfer from low to
higher energy regions. The CDW gap of 75~meV is observed at the lowest
temperature and shows significant deviations from an isotropic BCS-type
mean-field behavior. Absorption peaks appear at frequencies as low as
200~cm$^{-1}$ and can be identified with interband transitions according to
density-functional calculations. The change in the interband absorption
compared to KV$_3$Sb$_5$ reflects the inversion of band saddle points between
the K and Cs compounds. Additionally, a broader and strongly
temperature-dependent absorption feature is observed below 1000~cm$^{-1}$ and
assigned to a displaced Drude peak. It reflects localization effects on charge
carriers.
