ClearAll[rectangleFilling]
rectangleFilling[w_ : 12, op_ : .8, ef_ : Automatic] :=
ReplaceAll[
GraphicsComplex[c_, p_] :>
GraphicsComplex[c,
p /. Line[{a_, b_}, ___] :>
Dynamic @ {Opacity[1], Blend[{CurrentValue["Color"], White}, op],
EdgeForm[{AbsoluteThickness[2],
ef /. Automatic -> CurrentValue["Color"]}],
Rectangle[Offset[{-w, 0}, c[[b]]], Offset[{w, 0}, c[[a]]]]}]]
Examples:
rectangleFilling[]@
ListPlot[{1, 2, 3, 6, 4, 4}, Filling -> Bottom,
FillingStyle -> Directive[CapForm["Butt"], AbsoluteThickness[5]],
Frame -> True, GridLines -> Automatic,
PlotRangePadding -> {{-0.5, 0.5}, {0.5, 0.5}}]
rectangleFilling[20]@
ListPlot[MapIndexed[{{#2[[1]], #}} &]@{1, 2, 3, 6, 4, 4},
PlotStyle -> "Rainbow", Filling -> 2.5,
FillingStyle -> Directive[CapForm["Butt"], AbsoluteThickness[5]],
Frame -> True, GridLines -> Automatic,
PlotRangePadding -> {{-0.5, 0.5}, {0.5, 0.5}}]
Replace Filling -> 2.5} above with Filling -> {1 -> Top, 2 -> 5, 4 -> Bottom, 6 -> 2}` to get
