  We analyze the mass and width of the doubly heavy tetraquark $T_{ccs}$
composed of a heavy diquark and a light quark cloud with strangeness with
assuming that a color anti-triplet heavy diquark is a dominant component of the
doubly charmed tetraquarks $T_{cc}$ and $T_{ccs}$. We construct an effective
Lagrangian for masses of heavy hadrons based on the superflavor symmetry
between the doubly heavy tetraquarks and the singly heavy baryons with
including the terms which simultaneously break the heavy-quark and light flavor
symmetries, and predict the mass of $T_{ccs}$ as $M(T_{ccs}) = 4057\pm40$\,MeV.
The comparison of this prediction with future experimental observation will
give a clue to understand the color structure of the heavy diquark. We also
predict the spin-averaged mass of $\Omega_{cc}$ ($J^P = 1/2^+, 3/2^+)$ as
$M(\Omega_{cc}) = 3760\pm 18\,$MeV. We next calculate the decay width of
$T_{ccs}$, based on solely the light flavor symmetry, as $\Gamma(T_{ccs}) =
1.2\pm 0.3$\,MeV.
