diff --git a/src/gui/components/_legacy.py b/src/gui/components/_legacy.py
index fe5a581..402becf 100644
--- a/src/gui/components/_legacy.py
+++ b/src/gui/components/_legacy.py
@@ -628,22 +628,27 @@ def render_sticky_footer() -> None:
     st.markdown(
         """
 <style>
+/* DIAGNOSTIC: tint every plausible bottom-area container so we can
+   see WHICH element is actually filling the visible bottom of the
+   page. Whichever color shows in the "white bar" region is the
+   element to fix. To be reverted once the right target is known. */
 [data-testid="stAppViewBlockContainer"] {
-    /* Reserve room for the fixed footer overlay (footer min-height
-       32px + 0.25rem * 2 padding ≈ 2rem). */
-    padding-bottom: 2rem !important;
-    /* Stretch the container to at least viewport height so its own
-       background fills the area between the last piece of content
-       and the fixed footer overlay — otherwise ``.stApp``'s solid
-       white background shows through that gap and reads as a
-       horizontal "white bar". ``.stApp`` carries ``zoom: 0.85`` so
-       100vh in this layout renders at 85% visually; divide by 0.85
-       to span the full visible viewport. The footer itself is fixed
-       and lives outside ``.stApp`` (mounted on ``<body>``), so it's
-       not affected by the zoom and overlays normally. */
+    background: #ff5050 !important;    /* RED   = block container  */
     min-height: calc(100vh / 0.85) !important;
+    padding-bottom: 2rem !important;
     box-sizing: border-box !important;
 }
+[data-testid="stMain"],
+section[data-testid="stMain"] {
+    background: #50c0ff !important;    /* BLUE  = stMain           */
+    min-height: 100vh !important;
+}
+[data-testid="stAppViewContainer"] {
+    background: #50ff80 !important;    /* GREEN = view container   */
+}
+.stApp {
+    background: #ffd000 !important;    /* GOLD  = .stApp (zoomed)  */
+}
 #datatools-sticky-footer {
     position: fixed !important;
     bottom: 0 !important;
