I see. I tried
transform = torchvision.transforms.Compose([
torchvision.transforms.ToTensor(),
torchvision.transforms.Normalize(mean=mean/255, std=std/255)])

with
mean = 33.3184
std = 78.5675

but this gives me lower accuracy (0.88) than ToTensor() on its own (0.98). Is that expected for MNIST?