data <- data.frame(
  Group = sample(c("a", "b"), 50, replace = TRUE),
  value = rnorm(50, mean = 5, sd = 1)
)
ggplot(data, aes(x = Group, y = value, fill = Group, color = Group)) +
  geom_bar(stat = "summary", fun = "mean", 
           position = position_dodge(width = 0.5), size = 2,
           width = 0.4) +
  scale_color_manual(values = c("a" = "black", "b" = "black")) + 
  theme_minimal() +
  theme(legend.position = "none")