  We investigate the critical behavior of a near-critical fluid confined
between two parallel plates in contact with a reservoir by calculating the
order parameter profile and the Casimir amplitudes (for the force density and
for the grand potential). Our results are applicable to one-component fluids
and binary mixtures. We assume that the walls absorb one of the fluid
components selectively for binary mixtures. We propose a renormalized local
functional theory accounting for the fluctuation effects. Analysis is performed
in the plane of the temperature T and the order parameter in the reservoir
\psi_{\infty} . Our theory is universal if the physical quantities are scaled
appropriately. If the component favored by the walls is slightly poor in the
reservoir, there appears a line of first-order phase transition of capillary
condensation outside the bulk coexistence curve. The excess adsorp- tion
changes discontinuously between condensed and noncondensed states at the
transition. With increasing T, the transition line ends at a capillary critical
point T = T_c^{ca} slightly lower than the bulk critical temperature T_c. The
Casimir amplitudes are larger than their critical-point values by 10-100 times
between the transition line and the bulk coexistence curve and slightly above
the capillary critical point.
