# Visualizing Riemann sum for f(x,y): darker colors, axes in front

I'd like to create a picture for a Riemann sum for my Calculus class. I modified this example: http://reference.wolfram.com/language/example/Visualize3DRiemannSums.html#

and got this:

f = 20/(x^2 + y^2);
Grid[
Partition[
Table[
Show[
Quiet@DiscretePlot3D[f, {x, 1 + d/2, 2, d}, {y, 1 + d/2, 2, d},
ExtentSize -> Full,
FillingStyle -> Opacity[.6],
PlotStyle -> RGBColor[0.19, 1., 0.16]
],
PlotRange -> {{0, 2.3}, {0, 2.3}, {0, 10}},
ViewPoint -> {2, .5, 1.2},
Method -> {"AxesInFront" -> False},
Axes -> True, AxesOrigin -> {0, 0, 0}, AxesLabel -> None,
AxesStyle -> Directive[Thickness[0.001], Orange],
Lighting -> "Neutral",
ImageSize -> 500,
Boxed -> False,
AxesEdge -> {{1, -1}, {-1, -1}, {-1, 1}}],
{d, {1/2, 1/4, 1/8, 1/16}}],
2]
]


Unfortunately, the color for the plot is too dark, by some reason I can't make it lighter. Also, I do not like the axes in front of the picture. How can I fix that?

I am open to all suggestions on this topic: choice of a function, choice of a region, colors, etc. I guess, ultimately, I'd like to create the following picture:

I think this could be a starting point:

f = 20/(x^2 + y^2);
GraphicsGrid[
Partition[
Show[{DiscretePlot3D[f, {x, 1 + #/2, 2, #}, {y, 1 + #/2, 2, #},
ExtentSize -> Full, PlotStyle -> Cyan,
FillingStyle -> Opacity[1],
PlotRange -> {{0, 2.5}, {-1, 2.5}, {0, 12}}, Axes -> False,
AxesOrigin -> {0, 0, 0}, Ticks -> None, Boxed -> False,
ViewPoint -> {1.3, .7, .5}],
Graphics3D[{{Text[
Style["x", 24, Italic,
FontFamily -> "Times New Roman"], {2.4, 0, 0}]}, {Text[
Style["y", 24, Italic, FontFamily -> "Times New Roman"], {0,
2.4, 0}]}, {Text[
Style["z", 24, Italic, FontFamily -> "Times New Roman"], {0,
0, 12}]},
{Text[
Style["O", 24, Italic,
FontFamily -> "Times New Roman"], {0, -.5, 0}]},