Update app.py

app.py

@@ -1280,7 +1280,7 @@ def show_level_selection():
 def show_theme_selection():
     """Display theme selection interface"""
     # Header section
-        header_html = '''
+    header_html = '''
         <div style="text-align: center; margin-bottom: 2rem;">
             <h2 style="color: #1e88e5; font-family: 'Sarabun', sans-serif; margin: 0; display: flex; align-items: center; justify-content: center; gap: 8px;">
                 <span style="font-size: 1.5em;">🎨</span>