I am using this `ContourPlot`

`With[{n = 18}, Module[{colors}, colors = Join[{White}, (Lighter[Blue, #] & /@ Subdivide[1, 0, n])[[ 3 ;; -3]], {Black}]; ContourPlot[\[Alpha]1^2 \[Alpha]3^-1, {\[Alpha]3, 0, 0.8}, {\[Alpha]1, 0, 0.8}, AspectRatio -> 1, BaseStyle -> {FontSize -> 9}, FrameLabel -> {Style[\[Alpha]3, FontSize -> 14, Blue], Style[\[Alpha]1, FontSize -> 14, Blue]}, Contours -> Function[{min, max}, Range[Floor[min, -50], Ceiling[max, 50], 0.5]], ContourStyle -> {Dashed}, ContourShading -> {Black, Darker[Red, 0.6], Darker[Red, 0.4], Darker[Red, 0.2], Lighter[Red, 0.4], Lighter[Red, 0.75], Lighter[Red, 0.9], Lighter[Blue, 0.9], Lighter[Blue, 0.75], Lighter[Blue, 0.6], Lighter[Blue, 0.4], Lighter[Blue, 0.2], Blue, Darker[Blue, 0.2], Darker[Blue, 0.4], Darker[Blue, 0.6], Darker[Blue, 0.8]}, PlotLegends -> Automatic, ImageSize -> {Automatic, 500}, PlotRange -> All]]] `

The thing is, the left side of figure is kind of complicated. How can I reduce the contours in this area? In other words, how can I more decorate this plot and make it more professional?