double xc1, xc2, yc1,yc2;

void DrawClippedBox(double x1, double y1, double x2, double y2) {
   double X1=x1,X2=x2,Y1=y1,Y2=y2;
   if (X1<xc1) X1 = xc1;
   if (X2>xc2) X2 = xc2;
      if (Y1<yc1) Y1 = yc1;
   if (Y2>yc2) Y2 = yc2;
   auto b = new TBox(X1, Y1, X2, Y2);
   b->SetFillColor(kBlue);
   b->Draw();
}

void macro() {
   auto h = new TH1D("h", "h", 10, 0, 2);
   h->FillRandom("gaus", 10);
   h->Draw();

   xc1 = h->GetXaxis()->GetXmin();
   xc2 = h->GetXaxis()->GetXmax();
   yc1 = h->GetYaxis()->GetXmin();
   yc2 = h->GetYaxis()->GetXmax();

   DrawClippedBox(1, -2, 3, 1);

   gPad->RedrawAxis();
}