documentclass[twoside,a4paper]{tufte-handout}
%documentclass{article} %uncomment this to see what's happening
usepackage{tikz}

begin{document}
begin{tikzpicture}
small
draw[thick,blue,fill=blue!25]
        (0,1) coordinate (A)
    --  (3,1) coordinate (B)
    --  (5,2) coordinate (C)
    --  (5,4) coordinate (D)
    --  (3,4) coordinate (E)
    --  (2.5,3) coordinate (F)
    --  (2,4) coordinate (G)
    --  (0,4) coordinate (H)
    --cycle ;

draw[red,fill=red!25] (2.5,3.9) circle (.39) ;

end{tikzpicture}
end{document}