diff --git a/src/theme.rs b/src/theme.rs
index 0f87d6f..505939a 100644
--- a/src/theme.rs
+++ b/src/theme.rs
@@ -53,6 +53,22 @@ window.tour-window { background-color: transparent; }\n\
    the \"Show me\" fallback as its own beat, not a continuation of the \
    instructional paragraph above it. */\n\
 .tour-hint-row { margin-top: 8px; }\n\
+/* ui::troubleshoot_wizard — a bare gtk4::Window with no titlebar falls back \
+   to GTK's own minimal CSD (flat bar, plain system-font title, square \
+   corners), which read as a stray window from a different decade next to \
+   the rest of this (rounded, borderless) app. A real HeaderBar (set in \
+   troubleshoot_wizard::open) picks up the window's title automatically; \
+   this just makes it and the window match the shared dark theme instead \
+   of GTK's default light-grey CSD chrome. */\n\
+window.wizard-dialog { background-color: @bg; color: @on-bg; border-radius: 10px; }\n\
+window.wizard-dialog headerbar { \
+  background-color: @bg; \
+  color: @on-bg; \
+  border-top-left-radius: 10px; \
+  border-top-right-radius: 10px; \
+  border-bottom: 1px solid alpha(@on-bg, 0.08); \
+  box-shadow: none; \
+}\n\
 ";
 
 thread_local! {
diff --git a/src/ui/troubleshoot_wizard.rs b/src/ui/troubleshoot_wizard.rs
index e152678..f3c4bf2 100644
--- a/src/ui/troubleshoot_wizard.rs
+++ b/src/ui/troubleshoot_wizard.rs
@@ -37,6 +37,10 @@ pub fn open(parent: &impl IsA<gtk4::Window>, on_build: impl FnOnce(&Window)) {
         .default_width(480)
         .default_height(360)
         .build();
+    window.add_css_class("wizard-dialog");
+    let header = gtk4::HeaderBar::new();
+    header.set_show_title_buttons(true);
+    window.set_titlebar(Some(&header));
 
     let content = GBox::new(Orientation::Vertical, 12);
     content.add_css_class("view-content");