gROOT->ForceStyle(); -> gPad no more transparent

ROOT
1

I try to overlay a histogram where the pad is set logarithmic with a histogram that is not. Thus I tried to overlay a transparent pad. But forcing my style (maybe needed at some other places) it is not transparent anymore. What do I have to do? I’m using root 5.26

void canvasimage() {
   //create a canvas with a picture (.png,.jpg,.gif, etc) in the background
gROOT->SetStyle("Plain");
gROOT->ForceStyle();
   //TImage *img = TImage::Open("rose512.jpg");  //put your own picture here
   TCanvas *c1 = new TCanvas("c1");
   //img->Draw("x");
   TH1F *h1 = new TH1F("h1","test",100,-1,1);
   h1->SetFillColor(kRed);
   h1->FillRandom("gaus",3000);
	h1->Draw();
   
   //Create a transparent pad filling the full canvas
   TPad *p = new TPad("p","p",0,0,1,1);
   p->SetFillStyle(4000);
   p->SetFrameFillStyle(4000);
   p->Draw();
   p->cd();
   TH1F *h = new TH1F("h","test",100,-3,3);
   h->SetFillColor(kCyan);
   h->FillRandom("gaus",5000);
   h->Draw();
c1->Print("test.pdf");
}
2 
void canvasimage() {
   TCanvas *c1 = new TCanvas("c1");
   gROOT->SetStyle("Plain");
   gROOT->ForceStyle();
   gStyle->SetFrameFillColor(0);
   gStyle->SetFrameFillStyle(0);

   TH1F *h1 = new TH1F("h1","test",100,-1,1);
   h1->SetFillColor(kRed);
   h1->FillRandom("gaus",3000);
   h1->Draw();

   //Create a transparent pad filling the full canvas
   TPad *p = new TPad("p","p",0,0,1,1);
   p->SetFillStyle(4000);     
   p->Draw();
   p->cd();
   TH1F *h = new TH1F("h","test",100,-3,3);
   h->SetFillColor(kCyan);
   h->FillRandom("gaus",5000);
   h->Draw();
}
3

Big thanx