如何在ggplot中更改图例的样式，使每个元素周围都有一个矩形？

install.packages("ggplot2")
library(ggplot2)

data <- data.frame(x = c("A", "B", "C"), y = c(1, 2, 3))

ggplot(data, aes(x = x, y = y)) +

geom_bar(stat = "identity") +

theme(legend.key = element_rect(color = "black", fill = "white")) +

install.packages("ggplot2")
library(ggplot2)

data <- data.frame(x = c("A", "B", "C"), y = c(1, 2, 3))

ggplot(data, aes(x = x, y = y)) +
  geom_bar(stat = "identity") +
  theme(legend.key = element_rect(color = "black", fill = "white"))