I have below ggplot

library(ggplot2)
col_define = c('red', 'orange', 'blue', 'lightblue', 'green')
names(col_define) = as.vector(unique(diamonds$cut))

ggplot(diamonds, aes(color)) +
  geom_bar(aes(fill = cut)) +
  scale_fill_manual(values = col_define, breaks = names(col_define), aesthetics = c("fill")) + 
    theme(panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        legend.position=c(0,1),
        legend.justification = c(0,1),
        legend.box.margin = margin(5, l = 5, unit = 'mm'),
        legend.box = 'vertical',
        legend.box.background = element_rect( fill = alpha('#7f7f7f', .2), size = 0.1, linetype = "solid", color = "#595959"),
        axis.text.x = element_text(angle = 30, hjust = 1)
        ) 

As you can see, the legend does not appear to be in the right position. I want to place my legend in top-left position within the plot area, but there will be top-margin and left-margin of 5 pixel.

Additionally, the margin color and alpha value also do not appear to be correctly visible.

Could you please help how to correct them?