如何为ggplot2中facet_wrap的分面标题栏添加灰色粗边框？

需要给ggplot2中facet_wrap生成的分面标题栏（strip）添加与目标图一致的灰色粗边框。现有绘图效果、目标效果及当前代码如下：

当前绘图 #

目标绘图 #

当前代码 #

ggplot(data = melted_df, aes(sample = value, color = Distribution)) +
  stat_qq() +
  geom_qq_line() +
  facet_wrap(~Distribution, scales = "free") + xlab('Theoretical Quantiles') + 
  ylab('Sample Quantiles') + 
  ggtitle('QQ Plot for Different Distributions against Qnorm!') + 
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(), plot.title = element_text(size = 11),
        panel.background = element_rect(fill = "white"), legend.background=element_rect(fill = "lightgray"),
        legend.key = element_rect(fill = "lightgray"),
        axis.ticks.x = element_blank(),
        axis.ticks.y = element_blank(),
        legend.box.background = element_rect(color = "gray45", fill = NA, size=3),
        panel.border = element_rect(color = "gray45",fill = NA, size = 2), 
        strip.text = element_text(size = 10))

要实现目标效果，只需在theme()中添加分面标题栏的背景和边框设置即可，关键是配置strip.background和strip.border两个参数：

修改后的完整代码：

ggplot(data = melted_df, aes(sample = value, color = Distribution)) +
  stat_qq() +
  geom_qq_line() +
  facet_wrap(~Distribution, scales = "free") + 
  xlab('理论分位数') + 
  ylab('样本分位数') + 
  ggtitle('不同分布与正态分布的QQ图') + 
  theme(
    panel.grid.major = element_blank(), 
    panel.grid.minor = element_blank(), 
    plot.title = element_text(size = 11),
    panel.background = element_rect(fill = "white"), 
    legend.background = element_rect(fill = "lightgray"),
    legend.key = element_rect(fill = "lightgray"),
    axis.ticks.x = element_blank(),
    axis.ticks.y = element_blank(),
    legend.box.background = element_rect(color = "gray45", fill = NA, size=3),
    panel.border = element_rect(color = "gray45", fill = NA, size = 2), 
    strip.text = element_text(size = 10),
    # 新增分面标题栏样式设置
    strip.background = element_rect(fill = "lightgray"), # 匹配目标图的浅灰背景
    strip.border = element_rect(color = "gray45", fill = NA, size = 2) # 灰色粗边框
  )

参数说明 #

• strip.border：指定边框颜色为gray45（与现有面板边框颜色统一），fill=NA避免覆盖背景，size=2保证边框粗细和面板一致
• strip.background：给标题栏设置浅灰色背景，完全匹配目标图的视觉效果，如果不需要背景可删除该行

内容的提问来源于stack exchange，提问作者qqplotter