Extends the \newtheorem command. If you say \newshadetheorem{theorem}{Theorem} in the preamble then your regular \begin{theorem} .. \end{theorem} will produce a theorem statement in a shaded box. It supports all the options of \newtheorem, including forms \newshadetheorem{..}[..]{..} and \newshadetheorem{..}{..}[..]. Environments declared using the package require their body to remain on one page; the mdframed package can frame and shade theorems, and its environments break at the end of a page; users are generally recommended, therefore, to use mdframed. In the same spirit, the author told us in January 2020: “These materials are obsolete. There are a number of more recent, more powerful packages that have capabilities that greatly extend the simple ones here. A new project should use one of those. These files only continue to be available to help people who are working with an old project.”