ggplot2 Increase font size

Dear all,
I am using the code as below
  tdm <- melt(matrixToPlot)
   p<- ggplot(tdm, aes(x = Var2, y = Var1, fill = factor(value))) +
                  labs(x = "Mz", y = "T", fill = "D") +
                  geom_raster(alpha=1) +
                  scale_fill_discrete(h.start=1) +
                  scale_x_continuous(expand = c(0, 0)) +
                  scale_y_continuous(expand = c(0, 0))

to plot an two dimensional image .

I would like to ask your help to replace the gray border with white color
and increase the font size of x and y axis as wells as the legend of the
color bar. Could you please give me the function names to use?

Regards
Alex
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