Improve style

backend/app/program_content.py

@@ -25,6 +25,7 @@ def default_content_root() -> Path:
 
 
 CONTENT_ROOT = Path(os.getenv("PROGRAM_CONTENT_ROOT", default_content_root())).resolve()
+LESSON_BACKGROUND = "#f5f7fb"
 
 GRADE_ALIASES = {
     "CM1": "cm1",
@@ -134,6 +135,32 @@ def render_svg_section(path: Path, section_index: int) -> str:
         raise IndexError("Section introuvable")
     x, y, width, height = sections[section_index]["view_box"]
     text = path.read_text(encoding="utf-8", errors="ignore")
+    first_group_index = text.find("<g ")
+    if first_group_index > -1:
+        before_groups = text[:first_group_index]
+        after_groups = text[first_group_index:]
+        before_groups = re.sub(
+            r"\.bg\s*\{[^}]*\}",
+            f".bg {{ fill: {LESSON_BACKGROUND}; }}",
+            before_groups,
+            count=1,
+        )
+        before_groups = re.sub(
+            r"\.panel\s*\{[^}]*\}",
+            (
+                ".panel { fill: #ffffff; stroke: #d5e0dc; stroke-width: 3; "
+                "filter: drop-shadow(0 10px 24px rgba(22, 42, 45, 0.08)); }"
+            ),
+            before_groups,
+            count=1,
+        )
+        before_groups = re.sub(
+            r'(<rect\b(?=[^>]*class="panel")(?=[^>]*/>)[^>]*)/>',
+            rf'\1 style="fill:{LESSON_BACKGROUND};stroke:none;filter:none"/>',
+            before_groups,
+            count=1,
+        )
+        text = before_groups + after_groups
     text = re.sub(r'\swidth="[^"]+"', f' width="{int(width)}"', text, count=1)
     text = re.sub(r'\sheight="[^"]+"', f' height="{int(height)}"', text, count=1)
     text = re.sub(