Draw a thin border around each right-sidebar panel

src/ui/MainWindow.cpp

@@ -49,8 +49,8 @@ MainWindow::MainWindow(Simulation* sim, const std::string& configDir,
 
     m_sidePanel = new QWidget(this);
     QVBoxLayout* sideLayout = new QVBoxLayout(m_sidePanel);
-    sideLayout->setContentsMargins(0, 0, 0, 0);
+    sideLayout->setContentsMargins(1, 1, 1, 1);
-    sideLayout->setSpacing(0);
+    sideLayout->setSpacing(1);
 
     m_selectedBuildingPanel = new SelectedBuildingPanel(sim, &sim->config(), m_sidePanel);
     m_buildButtonGrid       = new BuildButtonGrid(&sim->config(), m_sidePanel);
@@ -60,6 +60,20 @@ MainWindow::MainWindow(Simulation* sim, const std::string& configDir,
     sideLayout->addWidget(m_buildButtonGrid,       1);
     sideLayout->addWidget(m_blueprintPanel,        1);
 
+    // Draw a thin border around each of the three side-panel sections. The class
+    // scoped selectors keep the border on the panels themselves rather than
+    // cascading onto their child widgets; WA_StyledBackground lets the plain
+    // QWidget subclasses honor the stylesheet box (border/background).
+    for (QWidget* panel : { static_cast<QWidget*>(m_selectedBuildingPanel),
+                            static_cast<QWidget*>(m_buildButtonGrid),
+                            static_cast<QWidget*>(m_blueprintPanel) })
+    {
+        panel->setAttribute(Qt::WA_StyledBackground, true);
+    }
+    m_sidePanel->setStyleSheet(QStringLiteral(
+        "SelectedBuildingPanel, BuildButtonGrid, BlueprintPanel {"
+        " border: 1px solid palette(mid); }"));
+
     m_gameWorldView->setFocus();
 
     connect(qApp, &QApplication::focusChanged, this, [this](QWidget*, QWidget* newWidget) {