  We study the spreading of droplets in a near-critical phase-separated liquid
mixture, using a combination of experiments, lubrication theory and
finite-element numerical simulations. The classical Tanner's law describing the
spreading of viscous droplets is robustly verified when the critical
temperature is neared. Furthermore, the microscopic cut-off length scale
emerging in this law is obtained as a single free parameter for each given
temperature. In total-wetting conditions, this length is interpreted as the
thickness of the thin precursor film present ahead of the apparent contact
line. The collapse of the different evolutions onto a single Tanner-like master
curve demonstrates the universality of viscous spreading before entering in the
fluctuation-dominated regime. Finally, our results reveal a counter-intuitive
and sharp thinning of the precursor film when approaching the critical
temperature, which is attributed to the vanishing spreading parameter at the
critical point.
