diff --git a/src/gui/_home.py b/src/gui/_home.py
index 1df4482..1078f80 100644
--- a/src/gui/_home.py
+++ b/src/gui/_home.py
@@ -174,7 +174,7 @@ def _home_page() -> None:
                 key=f"_home_remove_{digest}",
                 help=f"Remove {name}",
                 type="secondary",
-                use_container_width=True,
+                width="stretch",
             ):
                 to_remove = name
 
@@ -240,14 +240,14 @@ def _home_page() -> None:
             type="primary",
             key="home_run_analysis",
             disabled=not pending,
-            use_container_width=True,
+            width="stretch",
         )
     with col_clear:
         clear_clicked = st.button(
             t("upload.clear_results"),
             key="home_clear_results",
             disabled=not findings_by_file,
-            use_container_width=True,
+            width="stretch",
         )
 
     if clear_clicked:
diff --git a/src/gui/app_demo.py b/src/gui/app_demo.py
index abcc417..171436c 100644
--- a/src/gui/app_demo.py
+++ b/src/gui/app_demo.py
@@ -314,7 +314,7 @@ else:
 # ---------------------------------------------------------------------------
 
 st.markdown(f"#### BEFORE — {len(df_in)} rows, {len(df_in.columns)} columns")
-st.dataframe(df_in.head(10), use_container_width=True, hide_index=True)
+st.dataframe(df_in.head(10), width="stretch", hide_index=True)
 
 st.markdown("---")
 
@@ -338,7 +338,7 @@ st.markdown(pipe_summary)
 run_clicked = st.button(
     "▶ Run pipeline",
     type="primary",
-    use_container_width=True,
+    width="stretch",
     key="demo_run_button",
 )
 
@@ -404,7 +404,7 @@ if result is not None:
         )
     st.markdown("".join(pills_html), unsafe_allow_html=True)
 
-    st.dataframe(result.final_df.head(10), use_container_width=True, hide_index=True)
+    st.dataframe(result.final_df.head(10), width="stretch", hide_index=True)
 
     # ----- Download with watermark row -----
     watermark_row = pd.DataFrame([{
@@ -422,7 +422,7 @@ if result is not None:
             data=csv_bytes,
             file_name=Path(persona["data_file"]).stem + "_cleaned_demo.csv",
             mime="text/csv",
-            use_container_width=True,
+            width="stretch",
         )
     with col_cta:
         st.markdown(
diff --git a/src/gui/components/_legacy.py b/src/gui/components/_legacy.py
index 9d520fd..ab55992 100644
--- a/src/gui/components/_legacy.py
+++ b/src/gui/components/_legacy.py
@@ -215,7 +215,7 @@ def _render_diagnostics_sidebar() -> None:
                 "📂  Open log folder",
                 key="_diag_open_logs",
                 type="secondary",
-                use_container_width=True,
+                width="stretch",
             ):
                 opened = _open_in_file_manager(audit_log_dir(), select=log_path)
                 if not opened:
@@ -448,7 +448,7 @@ def local_download_button(
     mime: str = "application/octet-stream",  # noqa: ARG001 — kept for API compat
     disabled: bool = False,
     help: str | None = None,
-    use_container_width: bool = True,
+    width: str = "stretch",
 ) -> None:
     """Save bytes directly to the user's Downloads folder.
 
@@ -497,7 +497,7 @@ def local_download_button(
         disabled=disabled,
         help=help,
         type="secondary",
-        use_container_width=use_container_width,
+        width=width,
     )
 
     if clicked:
@@ -1412,7 +1412,7 @@ def match_group_card(
                 return styles
 
             styled = compare_df.style.apply(_highlight_diffs, axis=0)
-            st.dataframe(styled, use_container_width=True)
+            st.dataframe(styled, width="stretch")
 
             if len(keep_indices) == n_rows:
                 st.info("Decision: Kept All")
@@ -1470,7 +1470,7 @@ def match_group_card(
                 editor_df,
                 column_config=col_config,
                 disabled=disabled_cols,
-                use_container_width=True,
+                width="stretch",
                 hide_index=True,
                 key=f"editor_{gid}",
             )
@@ -1514,7 +1514,7 @@ def match_group_card(
                     columns=["Keep"],
                 ).reset_index(drop=True)
                 st.markdown("**Surviving rows preview:**")
-                st.dataframe(preview, use_container_width=True, hide_index=True)
+                st.dataframe(preview, width="stretch", hide_index=True)
 
             # Confirm
             def _on_confirm(
@@ -1848,7 +1848,7 @@ def render_findings_panel(
                     _t("findings.open_tool", tool=name),
                     key=f"_findings_open_{tool_id}_{ns}",
                     type="primary",
-                    use_container_width=False,
+                    width="content",
                 ):
                     st.switch_page(page_slug)
 
diff --git a/src/gui/pages/1_Deduplicator.py b/src/gui/pages/1_Deduplicator.py
index f9399a9..ae40532 100644
--- a/src/gui/pages/1_Deduplicator.py
+++ b/src/gui/pages/1_Deduplicator.py
@@ -192,7 +192,7 @@ if uploaded is not None:
             # markdown/caption/subheader collections.
             st.subheader(f"Preview: {uploaded.name}")
             st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-            st.dataframe(df.head(10), use_container_width=True)
+            st.dataframe(df.head(10), width="stretch")
 
         # Advanced options
         with st.expander("Options", expanded=not _has_result):
@@ -213,7 +213,7 @@ if uploaded is not None:
 
         st.divider()
 
-        if st.button("Find Duplicates", type="primary", use_container_width=True):
+        if st.button("Find Duplicates", type="primary", width="stretch"):
             progress_bar = st.progress(0, text="Comparing rows...")
 
             def _gui_progress(current: int, total: int) -> None:
@@ -350,7 +350,7 @@ if uploaded is not None:
                     if st.button(
                         "Apply Review Decisions & Download",
                         type="primary",
-                        use_container_width=True,
+                        width="stretch",
                     ):
                         reviewed_df, reviewed_removed = apply_review_decisions(
                             df, result.match_groups, decisions,
diff --git a/src/gui/pages/2_Text_Cleaner.py b/src/gui/pages/2_Text_Cleaner.py
index 9810c8c..1cc3ba4 100644
--- a/src/gui/pages/2_Text_Cleaner.py
+++ b/src/gui/pages/2_Text_Cleaner.py
@@ -119,7 +119,7 @@ with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
     if preview_show_hidden:
         render_hidden_aware_preview(df, n_rows=10)
     else:
-        st.dataframe(df.head(10), use_container_width=True)
+        st.dataframe(df.head(10), width="stretch")
 
 st.divider()
 
@@ -213,7 +213,7 @@ with st.expander("Options", expanded=not _has_result):
 
 st.divider()
 
-if st.button("Clean Text", type="primary", use_container_width=True):
+if st.button("Clean Text", type="primary", width="stretch"):
     with st.spinner("Cleaning..."):
         try:
             result = clean_dataframe(df, options)
@@ -280,7 +280,7 @@ if result.cells_changed:
     st.markdown("**Changes by column**")
     st.dataframe(
         counts.rename("cells_changed").to_frame(),
-        use_container_width=True,
+        width="stretch",
     )
 
     st.markdown("**Examples (first 25 changes)**")
@@ -326,7 +326,7 @@ if result.cells_changed:
             unsafe_allow_html=True,
         )
     else:
-        st.dataframe(examples, use_container_width=True, hide_index=True)
+        st.dataframe(examples, width="stretch", hide_index=True)
 
 st.markdown("**Cleaned preview (first 10 rows)**")
 # Reuse the same toggle the Examples table uses so the user controls both
@@ -334,7 +334,7 @@ st.markdown("**Cleaned preview (first 10 rows)**")
 if show_hidden:
     render_hidden_aware_preview(result.cleaned_df, n_rows=10)
 else:
-    st.dataframe(result.cleaned_df.head(10), use_container_width=True)
+    st.dataframe(result.cleaned_df.head(10), width="stretch")
 
 # ---------------------------------------------------------------------------
 # Downloads
diff --git a/src/gui/pages/3_Format_Standardizer.py b/src/gui/pages/3_Format_Standardizer.py
index dcaf139..c739dd1 100644
--- a/src/gui/pages/3_Format_Standardizer.py
+++ b/src/gui/pages/3_Format_Standardizer.py
@@ -107,7 +107,7 @@ except Exception as e:
 _has_result = st.session_state.get("fmtstd_result") is not None
 with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
     st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-    st.dataframe(df.head(10), use_container_width=True)
+    st.dataframe(df.head(10), width="stretch")
 st.divider()
 
 
@@ -478,7 +478,7 @@ with st.expander("Options", expanded=not _has_result):
             edited = st.data_editor(
                 starter,
                 num_rows="dynamic",
-                use_container_width=True,
+                width="stretch",
                 column_config={
                     "abbreviation": st.column_config.TextColumn(
                         "Short form",
@@ -530,7 +530,7 @@ run_disabled = not column_types
 if st.button(
     "Standardize Formats",
     type="primary",
-    use_container_width=True,
+    width="stretch",
     disabled=run_disabled,
 ):
     with st.spinner("Standardizing..."):
@@ -592,16 +592,16 @@ if result.cells_changed:
     st.markdown("**Changes by column**")
     st.dataframe(
         counts.rename("cells_changed").to_frame(),
-        use_container_width=True,
+        width="stretch",
     )
 
     st.markdown("**Examples (first 25 changes)**")
     examples = result.changes.head(25).copy()
     examples["row"] = examples["row"] + 1
-    st.dataframe(examples, use_container_width=True, hide_index=True)
+    st.dataframe(examples, width="stretch", hide_index=True)
 
 st.markdown("**Standardized preview (first 10 rows)**")
-st.dataframe(result.standardized_df.head(10), use_container_width=True)
+st.dataframe(result.standardized_df.head(10), width="stretch")
 
 
 # ---------------------------------------------------------------------------
diff --git a/src/gui/pages/4_Missing_Values.py b/src/gui/pages/4_Missing_Values.py
index 91e5180..9d67bbf 100644
--- a/src/gui/pages/4_Missing_Values.py
+++ b/src/gui/pages/4_Missing_Values.py
@@ -106,7 +106,7 @@ _has_result = st.session_state.get("missing_result") is not None
 
 with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
     st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-    st.dataframe(df.head(10), use_container_width=True)
+    st.dataframe(df.head(10), width="stretch")
 
 st.divider()
 
@@ -134,7 +134,7 @@ with st.expander("Options", expanded=not _has_result):
     m3.metric("% cells missing", f"{initial_profile.cells_missing_pct:.1f}%")
     m4.metric("Complete rows", initial_profile.rows_complete)
 
-    st.dataframe(prof_df, use_container_width=True, hide_index=True)
+    st.dataframe(prof_df, width="stretch", hide_index=True)
 
     if initial_profile.cells_missing == 0:
         st.success("No missing values or disguised nulls detected. Nothing to handle.")
@@ -259,7 +259,7 @@ with st.expander("Options", expanded=not _has_result):
             })
             edited = st.data_editor(
                 edit_df,
-                use_container_width=True,
+                width="stretch",
                 hide_index=True,
                 column_config={
                     "column": st.column_config.TextColumn("Column", disabled=True),
@@ -285,7 +285,7 @@ with st.expander("Options", expanded=not _has_result):
 
 st.divider()
 
-if st.button("Handle Missing Values", type="primary", use_container_width=True):
+if st.button("Handle Missing Values", type="primary", width="stretch"):
     with st.spinner("Handling..."):
         try:
             result = handle_missing(df, options)
@@ -345,25 +345,25 @@ after = result.profile_after.to_dataframe().set_index("column")[
     ["missing", "missing_pct"]
 ].rename(columns={"missing": "after_missing", "missing_pct": "after_pct"})
 combined = before.join(after, how="outer").fillna(0)
-st.dataframe(combined, use_container_width=True)
+st.dataframe(combined, width="stretch")
 
 if result.strategy_per_column:
     st.markdown("**Strategy applied per column**")
     strat_df = pd.DataFrame(
         [{"column": c, "strategy": s} for c, s in result.strategy_per_column.items()]
     )
-    st.dataframe(strat_df, use_container_width=True, hide_index=True)
+    st.dataframe(strat_df, width="stretch", hide_index=True)
 
 if not result.changes.empty:
     st.markdown("**Audit (first 50 changes)**")
     audit_view = result.changes.head(50).copy()
     audit_view["row"] = audit_view["row"].apply(lambda x: "—" if x == -1 else x + 1)
-    st.dataframe(audit_view, use_container_width=True, hide_index=True)
+    st.dataframe(audit_view, width="stretch", hide_index=True)
     if len(result.changes) > 50:
         st.caption(f"… and {len(result.changes) - 50} more (download the full audit below).")
 
 st.markdown("**Handled preview (first 10 rows)**")
-st.dataframe(result.handled_df.head(10), use_container_width=True)
+st.dataframe(result.handled_df.head(10), width="stretch")
 
 # ---------------------------------------------------------------------------
 # Downloads
diff --git a/src/gui/pages/5_Column_Mapper.py b/src/gui/pages/5_Column_Mapper.py
index 28667d0..ea68311 100644
--- a/src/gui/pages/5_Column_Mapper.py
+++ b/src/gui/pages/5_Column_Mapper.py
@@ -98,7 +98,7 @@ _has_result = st.session_state.get("colmap_result") is not None
 
 with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
     st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-    st.dataframe(df.head(10), use_container_width=True)
+    st.dataframe(df.head(10), width="stretch")
 st.divider()
 
 # ---------------------------------------------------------------------------
@@ -165,7 +165,7 @@ with st.expander("Options", expanded=not _has_result):
         })
         edited = st.data_editor(
             initial,
-            use_container_width=True,
+            width="stretch",
             num_rows="dynamic",
             column_config={
                 "name": st.column_config.TextColumn("Target name"),
@@ -276,7 +276,7 @@ with st.expander("Options", expanded=not _has_result):
         })
         rename_edited = st.data_editor(
             rename_initial,
-            use_container_width=True,
+            width="stretch",
             column_config={
                 "source": st.column_config.TextColumn("Source", disabled=True),
                 "target": st.column_config.TextColumn("Target"),
@@ -304,7 +304,7 @@ with st.expander("Options", expanded=not _has_result):
         })
         map_edited = st.data_editor(
             map_initial,
-            use_container_width=True,
+            width="stretch",
             column_config={
                 "source": st.column_config.TextColumn("Source", disabled=True),
                 "target": st.column_config.SelectboxColumn(
@@ -332,7 +332,7 @@ with st.expander("Options", expanded=not _has_result):
 
 st.divider()
 
-if st.button("Apply Column Mapping", type="primary", use_container_width=True):
+if st.button("Apply Column Mapping", type="primary", width="stretch"):
     with st.spinner("Mapping..."):
         try:
             result = map_columns(df, options)
@@ -400,10 +400,10 @@ if result.mapping:
             for s, t in result.mapping.items()
         ],
     )
-    st.dataframe(map_df, use_container_width=True, hide_index=True)
+    st.dataframe(map_df, width="stretch", hide_index=True)
 
 st.markdown("**Mapped preview (first 10 rows)**")
-st.dataframe(result.mapped_df.head(10), use_container_width=True)
+st.dataframe(result.mapped_df.head(10), width="stretch")
 
 # ---------------------------------------------------------------------------
 # Downloads
diff --git a/src/gui/pages/6_Outlier_Detector.py b/src/gui/pages/6_Outlier_Detector.py
index 6949fb4..8b1ae22 100644
--- a/src/gui/pages/6_Outlier_Detector.py
+++ b/src/gui/pages/6_Outlier_Detector.py
@@ -72,7 +72,7 @@ if uploaded is not None:
             df = pd.read_csv(uploaded)
         st.subheader(f"Preview: {uploaded.name}")
         st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-        st.dataframe(df.head(10), use_container_width=True)
+        st.dataframe(df.head(10), width="stretch")
     except Exception as e:
         from src.core.errors import format_for_user
         st.error(
@@ -95,5 +95,5 @@ st.subheader("Handling")
 st.selectbox("Action", ["Flag only (add column)", "Remove outlier rows", "Cap / Winsorize to bounds"], disabled=True)
 
 st.divider()
-st.button("Detect Outliers", type="primary", use_container_width=True, disabled=True)
+st.button("Detect Outliers", type="primary", width="stretch", disabled=True)
 
diff --git a/src/gui/pages/7_Multi_File_Merger.py b/src/gui/pages/7_Multi_File_Merger.py
index fc6594f..fd526c9 100644
--- a/src/gui/pages/7_Multi_File_Merger.py
+++ b/src/gui/pages/7_Multi_File_Merger.py
@@ -74,7 +74,7 @@ if uploaded_files:
                 df = pd.read_csv(f)
             st.subheader(f"Preview: {f.name}")
             st.caption(f"{len(df)} rows, {len(df.columns)} columns — Columns: {', '.join(df.columns[:10])}{'...' if len(df.columns) > 10 else ''}")
-            st.dataframe(df.head(5), use_container_width=True)
+            st.dataframe(df.head(5), width="stretch")
         except Exception as e:
             from src.core.errors import format_for_user
             st.error(
@@ -93,5 +93,5 @@ st.selectbox("Mismatched columns", ["Fill with null", "Drop non-shared columns",
 st.checkbox("Add source filename column", value=True, disabled=True)
 
 st.divider()
-st.button("Merge Files", type="primary", use_container_width=True, disabled=True)
+st.button("Merge Files", type="primary", width="stretch", disabled=True)
 
diff --git a/src/gui/pages/8_Validator_Reporter.py b/src/gui/pages/8_Validator_Reporter.py
index 2b80502..8cb8887 100644
--- a/src/gui/pages/8_Validator_Reporter.py
+++ b/src/gui/pages/8_Validator_Reporter.py
@@ -72,7 +72,7 @@ if uploaded is not None:
             df = pd.read_csv(uploaded)
         st.subheader(f"Preview: {uploaded.name}")
         st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-        st.dataframe(df.head(10), use_container_width=True)
+        st.dataframe(df.head(10), width="stretch")
     except Exception as e:
         from src.core.errors import format_for_user
         st.error(
@@ -100,5 +100,5 @@ st.subheader("Report Format")
 st.selectbox("Output format", ["Excel (flagged rows)", "PDF summary", "Both"], disabled=True)
 
 st.divider()
-st.button("Validate & Generate Report", type="primary", use_container_width=True, disabled=True)
+st.button("Validate & Generate Report", type="primary", width="stretch", disabled=True)
 
diff --git a/src/gui/pages/9_Pipeline_Runner.py b/src/gui/pages/9_Pipeline_Runner.py
index fd02dfd..b035fd1 100644
--- a/src/gui/pages/9_Pipeline_Runner.py
+++ b/src/gui/pages/9_Pipeline_Runner.py
@@ -99,7 +99,7 @@ _has_result = st.session_state.get("pipeline_result") is not None
 
 with st.expander(f"Preview: {uploaded.name}", expanded=not _has_result):
     st.caption(f"{len(df)} rows, {len(df.columns)} columns")
-    st.dataframe(df.head(10), use_container_width=True)
+    st.dataframe(df.head(10), width="stretch")
 
 st.divider()
 
@@ -170,7 +170,7 @@ with st.expander("Options", expanded=not _has_result):
     )
     edited = st.data_editor(
         st.session_state["pipeline_rows"],
-        use_container_width=True,
+        width="stretch",
         num_rows="dynamic",
         column_config={
             "tool": st.column_config.SelectboxColumn(
@@ -246,7 +246,7 @@ run_disabled = current_pipeline is None or not current_pipeline.steps
 if st.button(
     "Run Pipeline",
     type="primary",
-    use_container_width=True,
+    width="stretch",
     disabled=run_disabled,
 ):
     progress = st.progress(0.0, text="Starting...")
@@ -343,10 +343,10 @@ step_df = pd.DataFrame([
     }
     for sr in result.step_results
 ])
-st.dataframe(step_df, use_container_width=True, hide_index=True)
+st.dataframe(step_df, width="stretch", hide_index=True)
 
 st.markdown("**Output preview (first 10 rows)**")
-st.dataframe(result.final_df.head(10), use_container_width=True)
+st.dataframe(result.final_df.head(10), width="stretch")
 
 # ---------------------------------------------------------------------------
 # Downloads