Here is how I am plotting the three implicit functions:
Show [ ContourPlot[f[h, a] == 0, {a, 0, 0.6}, {h, 0, 1},
ContourStyle -> Black],
ContourPlot[f2[h, a] == 0, {a, 0, 0.6}, {h, 0, 1},
ContourStyle -> Red],
ContourPlot[f3[h, a] == 0, {a, 0, 0.6}, {h, 0, 1},
ContourStyle -> Blue] ]
This works fine but I would like to add a legend, axis labels, larger fonts for the axes etc. I am using Mathematica 11.