fix: inherit plot background color in logo compositing

The logo grob uses theme_void() (transparent background), so when
arrangeGrob() composites it with a dark-themed plot, the logo strip
falls back to the device default (white). Extract the plot's
plot.background fill and apply it to the logo grob before compositing.

Fixes the issue where theme_civilytics_dark(font_size = 16) piped to
civilytics_logo(variant = "dark") would show a light background in
the logo/caption area.

R/logo.R

@@ -64,6 +64,16 @@ add_logo <- function(plot, logo, margin_param = NULL, font_scale = 1.1,
   position <- match.arg(position)
   at_top <- grepl("top", position)
 
+  # Inherit the plot's background color so the logo strip matches.
+  # make_logo_grob() uses theme_void() (transparent), so without this the
+  # logo area falls back to the device default (white).
+  bg_fill <- plot$theme$plot.background$fill
+  if (!is.null(bg_fill) && !is.na(bg_fill)) {
+    logo <- logo + ggplot2::theme(
+      plot.background = ggplot2::element_rect(fill = bg_fill, color = NA)
+    )
+  }
+
   # Inflate text sizes to compensate for arrangeGrob viewport shrinkage.
   # All theme text elements use rel() sizing, so scaling the root 'text'
   # element cascades to titles, axis labels, legends, captions, and strips.
@@ -164,6 +174,14 @@ has_caption <- function(gg) {
 #' }
 add_logo_ga <- function(plot_list, logo, nrow = 1, widths = NULL,
                         margin_param = NULL, font_scale = 1.1) {
+  # Inherit the background color from the first plot so the logo strip matches
+  bg_fill <- plot_list[[1]]$theme$plot.background$fill
+  if (!is.null(bg_fill) && !is.na(bg_fill)) {
+    logo <- logo + ggplot2::theme(
+      plot.background = ggplot2::element_rect(fill = bg_fill, color = NA)
+    )
+  }
+
   # Inflate text sizes to compensate for viewport shrinkage
   if (!is.null(font_scale) && font_scale != 1) {
     plot_list <- lapply(plot_list, function(p) {