We present a progress report on our calculation of the decay constants
$f_B$ and $f_{B_s}$ from lattice-QCD simulations with highly-improved staggered quarks.
Simulations are carried out with several heavy valence-quark masses on
$(2+1+1)$-flavor ensembles that include charm sea quarks.
We include data at six lattice spacings and several light sea-quark masses,
including an approximately physical-mass ensemble at all but the smallest lattice spacing, 0.03 fm.
This range of parameters provides excellent control of the continuum extrapolation to zero lattice spacing
and of heavy-quark discretization errors.
Finally, using the heavy-quark effective theory expansion
we present a method of extracting from the same correlation functions
the charm- and bottom-quark masses as well as some low-energy constants
appearing in the heavy-quark expansion.