diff --git a/main.py b/main.py
index abe1c15..fce11a5 100644
--- a/main.py
+++ b/main.py
@@ -418,9 +418,10 @@ def sync_board_state():
                 header_label.set_text(CLOSED_HEADER_TEXT)
                 header_label.update()
 
-            # Hide all board views
+            # Show closed message in all board views
             for view_key, (container, _) in board_views.items():
-                container.style("display: none;")
+                container.clear()
+                build_closed_message(container)
                 container.update()
 
             # Make sure controls row is showing only the Start New Game button
@@ -915,9 +916,39 @@ def generate_new_board():
     reset_board()
 
 
+def build_closed_message(parent):
+    """
+    Build a message indicating the game is closed, to be displayed in place of the board.
+
+    Args:
+        parent: The parent UI element to build the message in
+    """
+    with parent:
+        with ui.element("div").classes(GRID_CONTAINER_CLASS):
+            with ui.element("div").classes(
+                "flex justify-center items-center h-full w-full"
+            ):
+                ui.label("GAME CLOSED").classes("text-center fit-header").style(
+                    f"font-family: {HEADER_FONT_FAMILY}; color: {FREE_SPACE_TEXT_COLOR}; font-size: 6rem;"
+                )
+
+    # Run JavaScript to ensure text is resized properly
+    try:
+        js_code = """
+            setTimeout(function() {
+                if (typeof fitty !== 'undefined') {
+                    fitty('.fit-header', { multiLine: true, minSize: 10, maxSize: 2000 });
+                }
+            }, 50);
+        """
+        ui.run_javascript(js_code)
+    except Exception as e:
+        logging.debug(f"JavaScript execution failed: {e}")
+
+
 def close_game():
     """
-    Close the game - hide the board and update the header text.
+    Close the game - show closed message instead of the board and update the header text.
     This function is called when the close button is clicked.
     """
     global is_game_closed, header_label
@@ -928,9 +959,10 @@ def close_game():
         header_label.set_text(CLOSED_HEADER_TEXT)
         header_label.update()
 
-    # Hide all board views (both home and stream)
+    # Show closed message in all board views
     for view_key, (container, tile_buttons_local) in board_views.items():
-        container.style("display: none;")
+        container.clear()
+        build_closed_message(container)
         container.update()
 
     # Modify the controls row to only show the New Board button
diff --git a/poetry.lock b/poetry.lock
index d37c574..b7e0c41 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1166,6 +1166,59 @@ files = [
     {file = "multidict-6.1.0.tar.gz", hash = "sha256:22ae2ebf9b0c69d206c003e2f6a914ea33f0a932d4aa16f236afc049d9958f4a"},
 ]
 
+[[package]]
+name = "mypy"
+version = "1.15.0"
+description = "Optional static typing for Python"
+optional = false
+python-versions = ">=3.9"
+groups = ["dev"]
+files = [
+    {file = "mypy-1.15.0-cp310-cp310-macosx_10_9_x86_64.whl", hash = "sha256:979e4e1a006511dacf628e36fadfecbcc0160a8af6ca7dad2f5025529e082c13"},
+    {file = "mypy-1.15.0-cp310-cp310-macosx_11_0_arm64.whl", hash = "sha256:c4bb0e1bd29f7d34efcccd71cf733580191e9a264a2202b0239da95984c5b559"},
+    {file = "mypy-1.15.0-cp310-cp310-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:be68172e9fd9ad8fb876c6389f16d1c1b5f100ffa779f77b1fb2176fcc9ab95b"},
+    {file = "mypy-1.15.0-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:c7be1e46525adfa0d97681432ee9fcd61a3964c2446795714699a998d193f1a3"},
+    {file = "mypy-1.15.0-cp310-cp310-musllinux_1_2_x86_64.whl", hash = "sha256:2e2c2e6d3593f6451b18588848e66260ff62ccca522dd231cd4dd59b0160668b"},
+    {file = "mypy-1.15.0-cp310-cp310-win_amd64.whl", hash = "sha256:6983aae8b2f653e098edb77f893f7b6aca69f6cffb19b2cc7443f23cce5f4828"},
+    {file = "mypy-1.15.0-cp311-cp311-macosx_10_9_x86_64.whl", hash = "sha256:2922d42e16d6de288022e5ca321cd0618b238cfc5570e0263e5ba0a77dbef56f"},
+    {file = "mypy-1.15.0-cp311-cp311-macosx_11_0_arm64.whl", hash = "sha256:2ee2d57e01a7c35de00f4634ba1bbf015185b219e4dc5909e281016df43f5ee5"},
+    {file = "mypy-1.15.0-cp311-cp311-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:973500e0774b85d9689715feeffcc980193086551110fd678ebe1f4342fb7c5e"},
+    {file = "mypy-1.15.0-cp311-cp311-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:5a95fb17c13e29d2d5195869262f8125dfdb5c134dc8d9a9d0aecf7525b10c2c"},
+    {file = "mypy-1.15.0-cp311-cp311-musllinux_1_2_x86_64.whl", hash = "sha256:1905f494bfd7d85a23a88c5d97840888a7bd516545fc5aaedff0267e0bb54e2f"},
+    {file = "mypy-1.15.0-cp311-cp311-win_amd64.whl", hash = "sha256:c9817fa23833ff189db061e6d2eff49b2f3b6ed9856b4a0a73046e41932d744f"},
+    {file = "mypy-1.15.0-cp312-cp312-macosx_10_13_x86_64.whl", hash = "sha256:aea39e0583d05124836ea645f412e88a5c7d0fd77a6d694b60d9b6b2d9f184fd"},
+    {file = "mypy-1.15.0-cp312-cp312-macosx_11_0_arm64.whl", hash = "sha256:2f2147ab812b75e5b5499b01ade1f4a81489a147c01585cda36019102538615f"},
+    {file = "mypy-1.15.0-cp312-cp312-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:ce436f4c6d218a070048ed6a44c0bbb10cd2cc5e272b29e7845f6a2f57ee4464"},
+    {file = "mypy-1.15.0-cp312-cp312-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:8023ff13985661b50a5928fc7a5ca15f3d1affb41e5f0a9952cb68ef090b31ee"},
+    {file = "mypy-1.15.0-cp312-cp312-musllinux_1_2_x86_64.whl", hash = "sha256:1124a18bc11a6a62887e3e137f37f53fbae476dc36c185d549d4f837a2a6a14e"},
+    {file = "mypy-1.15.0-cp312-cp312-win_amd64.whl", hash = "sha256:171a9ca9a40cd1843abeca0e405bc1940cd9b305eaeea2dda769ba096932bb22"},
+    {file = "mypy-1.15.0-cp313-cp313-macosx_10_13_x86_64.whl", hash = "sha256:93faf3fdb04768d44bf28693293f3904bbb555d076b781ad2530214ee53e3445"},
+    {file = "mypy-1.15.0-cp313-cp313-macosx_11_0_arm64.whl", hash = "sha256:811aeccadfb730024c5d3e326b2fbe9249bb7413553f15499a4050f7c30e801d"},
+    {file = "mypy-1.15.0-cp313-cp313-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:98b7b9b9aedb65fe628c62a6dc57f6d5088ef2dfca37903a7d9ee374d03acca5"},
+    {file = "mypy-1.15.0-cp313-cp313-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:c43a7682e24b4f576d93072216bf56eeff70d9140241f9edec0c104d0c515036"},
+    {file = "mypy-1.15.0-cp313-cp313-musllinux_1_2_x86_64.whl", hash = "sha256:baefc32840a9f00babd83251560e0ae1573e2f9d1b067719479bfb0e987c6357"},
+    {file = "mypy-1.15.0-cp313-cp313-win_amd64.whl", hash = "sha256:b9378e2c00146c44793c98b8d5a61039a048e31f429fb0eb546d93f4b000bedf"},
+    {file = "mypy-1.15.0-cp39-cp39-macosx_10_9_x86_64.whl", hash = "sha256:e601a7fa172c2131bff456bb3ee08a88360760d0d2f8cbd7a75a65497e2df078"},
+    {file = "mypy-1.15.0-cp39-cp39-macosx_11_0_arm64.whl", hash = "sha256:712e962a6357634fef20412699a3655c610110e01cdaa6180acec7fc9f8513ba"},
+    {file = "mypy-1.15.0-cp39-cp39-manylinux_2_17_aarch64.manylinux2014_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:f95579473af29ab73a10bada2f9722856792a36ec5af5399b653aa28360290a5"},
+    {file = "mypy-1.15.0-cp39-cp39-manylinux_2_17_x86_64.manylinux2014_x86_64.manylinux_2_28_x86_64.whl", hash = "sha256:8f8722560a14cde92fdb1e31597760dc35f9f5524cce17836c0d22841830fd5b"},
+    {file = "mypy-1.15.0-cp39-cp39-musllinux_1_2_x86_64.whl", hash = "sha256:1fbb8da62dc352133d7d7ca90ed2fb0e9d42bb1a32724c287d3c76c58cbaa9c2"},
+    {file = "mypy-1.15.0-cp39-cp39-win_amd64.whl", hash = "sha256:d10d994b41fb3497719bbf866f227b3489048ea4bbbb5015357db306249f7980"},
+    {file = "mypy-1.15.0-py3-none-any.whl", hash = "sha256:5469affef548bd1895d86d3bf10ce2b44e33d86923c29e4d675b3e323437ea3e"},
+    {file = "mypy-1.15.0.tar.gz", hash = "sha256:404534629d51d3efea5c800ee7c42b72a6554d6c400e6a79eafe15d11341fd43"},
+]
+
+[package.dependencies]
+mypy_extensions = ">=1.0.0"
+typing_extensions = ">=4.6.0"
+
+[package.extras]
+dmypy = ["psutil (>=4.0)"]
+faster-cache = ["orjson"]
+install-types = ["pip"]
+mypyc = ["setuptools (>=50)"]
+reports = ["lxml"]
+
 [[package]]
 name = "mypy-extensions"
 version = "1.0.0"
@@ -2519,4 +2572,4 @@ propcache = ">=0.2.0"
 [metadata]
 lock-version = "2.1"
 python-versions = "^3.12"
-content-hash = "4377469668b11d516a06d64aaf4418b1c2d606eb21a383eeb40ebaa45c5d14a0"
+content-hash = "ea0dbf94f60bfaba1db5ac89c63c3c8ce3510f60659ba6c778c19c55dd29531f"
diff --git a/pyproject.toml b/pyproject.toml
index 47ff759..a28c0ce 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,6 +20,7 @@ flake8 = "^7.0.0"
 black = "^24.2.0"
 isort = "^5.13.2"
 python-semantic-release = "^9.1.1"
+mypy = "^1.15.0"
 
 [build-system]
 requires = ["poetry-core>=1.8"]
diff --git a/src/config/constants.py b/src/config/constants.py
index 6d668cb..5853f97 100644
--- a/src/config/constants.py
+++ b/src/config/constants.py
@@ -2,40 +2,53 @@
 Configuration constants for the Bingo application.
 """
 
+from typing import Final, Literal
+
+# Type definitions for CSS properties
+CssColor = str  # Hex color code like "#123456" or named color like "red"
+CssFontFamily = str  # Font family names like "'Font Name', sans-serif"
+CssFontWeight = str  # Font weight like "400", "700", etc.
+CssFontStyle = Literal["normal", "italic", "oblique"]
+CssClass = str  # CSS class name or space-separated class names
+
 # Header text and display settings
-HEADER_TEXT = "COMMIT !BINGO"
-HEADER_TEXT_COLOR = "#0CB2B3"
-CLOSED_HEADER_TEXT = "Bingo Is Closed"
+HEADER_TEXT: Final[str] = "COMMIT !BINGO"
+HEADER_TEXT_COLOR: Final[CssColor] = "#0CB2B3"
+CLOSED_HEADER_TEXT: Final[str] = "Bingo Is Closed"
+CLOSED_MESSAGE_TEXT: Final[str] = "GAME CLOSED"
+CLOSED_MESSAGE_COLOR: Final[CssColor] = "#FF7f33"
 
 # Free space settings
-FREE_SPACE_TEXT = "FREE MEAT"
-FREE_SPACE_TEXT_COLOR = "#FF7f33"
+FREE_SPACE_TEXT: Final[str] = "FREE MEAT"
+FREE_SPACE_TEXT_COLOR: Final[CssColor] = "#FF7f33"
 
 # Tile appearance settings
-TILE_CLICKED_BG_COLOR = "#100079"
-TILE_CLICKED_TEXT_COLOR = "#1BEFF5"
-TILE_UNCLICKED_BG_COLOR = "#1BEFF5"
-TILE_UNCLICKED_TEXT_COLOR = "#100079"
+TILE_CLICKED_BG_COLOR: Final[CssColor] = "#100079"
+TILE_CLICKED_TEXT_COLOR: Final[CssColor] = "#1BEFF5"
+TILE_UNCLICKED_BG_COLOR: Final[CssColor] = "#1BEFF5"
+TILE_UNCLICKED_TEXT_COLOR: Final[CssColor] = "#100079"
 
 # Page backgrounds
-HOME_BG_COLOR = "#100079"
-STREAM_BG_COLOR = "#00FF00"
+HOME_BG_COLOR: Final[CssColor] = "#100079"
+STREAM_BG_COLOR: Final[CssColor] = "#00FF00"
 
 # Font settings
-HEADER_FONT_FAMILY = "'Super Carnival', sans-serif"
-BOARD_TILE_FONT = "Inter"
-BOARD_TILE_FONT_WEIGHT = "700"
-BOARD_TILE_FONT_STYLE = "normal"
+HEADER_FONT_FAMILY: Final[CssFontFamily] = "'Super Carnival', sans-serif"
+BOARD_TILE_FONT: Final[str] = "Inter"
+BOARD_TILE_FONT_WEIGHT: Final[CssFontWeight] = "700"
+BOARD_TILE_FONT_STYLE: Final[CssFontStyle] = "normal"
 
 # UI Class Constants
-BOARD_CONTAINER_CLASS = "flex justify-center items-center w-full"
-HEADER_CONTAINER_CLASS = "w-full"
-CARD_CLASSES = (
+BOARD_CONTAINER_CLASS: Final[CssClass] = "flex justify-center items-center w-full"
+HEADER_CONTAINER_CLASS: Final[CssClass] = "w-full"
+CARD_CLASSES: Final[CssClass] = (
     "relative p-2 rounded-xl shadow-8 w-full h-full flex items-center justify-center"
 )
-COLUMN_CLASSES = "flex flex-col items-center justify-center gap-0 w-full"
-GRID_CONTAINER_CLASS = "w-full aspect-square p-4"
-GRID_CLASSES = "gap-2 h-full grid-rows-5"
-ROW_CLASSES = "w-full"
-LABEL_SMALL_CLASSES = "fit-text-small text-center select-none"
-LABEL_CLASSES = "fit-text text-center select-none"
+COLUMN_CLASSES: Final[CssClass] = (
+    "flex flex-col items-center justify-center gap-0 w-full"
+)
+GRID_CONTAINER_CLASS: Final[CssClass] = "w-full aspect-square p-4"
+GRID_CLASSES: Final[CssClass] = "gap-2 h-full grid-rows-5"
+ROW_CLASSES: Final[CssClass] = "w-full"
+LABEL_SMALL_CLASSES: Final[CssClass] = "fit-text-small text-center select-none"
+LABEL_CLASSES: Final[CssClass] = "fit-text text-center select-none"
diff --git a/src/core/game_logic.py b/src/core/game_logic.py
index a751d0f..7f30927 100644
--- a/src/core/game_logic.py
+++ b/src/core/game_logic.py
@@ -5,6 +5,7 @@
 import datetime
 import logging
 import random
+from typing import List, Optional, Set, cast
 
 from nicegui import ui
 
@@ -18,27 +19,46 @@
     TILE_UNCLICKED_BG_COLOR,
     TILE_UNCLICKED_TEXT_COLOR,
 )
+from src.types.ui_types import (
+    BingoPattern,
+    BingoPatterns,
+    BoardType,
+    BoardViews,
+    ClickedTiles,
+    Coordinate,
+    TileButtonsDict,
+    TileLabelInfo,
+)
 from src.utils.text_processing import get_line_style_for_lines, split_phrase_into_lines
 
 # Global variables for game state
-board = []  # 2D array of phrases
-clicked_tiles = set()  # Set of (row, col) tuples that are clicked
-bingo_patterns = set()  # Set of winning patterns found
-board_iteration = 1
-is_game_closed = False
-today_seed = None
+board: BoardType = []  # 2D array of phrases
+clicked_tiles: ClickedTiles = set()  # Set of (row, col) tuples that are clicked
+bingo_patterns: BingoPatterns = set()  # Set of winning patterns found
+board_iteration: int = 1
+is_game_closed: bool = False
+today_seed: Optional[str] = None
 
 # Global variables for UI references (initialized in the UI module)
-header_label = None
-controls_row = None
-seed_label = None
-board_views = {}  # Dictionary mapping view name to (container, tile_buttons) tuple
+header_label: Optional[ui.label] = None
+controls_row: Optional[ui.row] = None
+seed_label: Optional[ui.label] = None
+board_views: BoardViews = (
+    {}
+)  # Dictionary mapping view name to (container, tile_buttons) tuple
 
 
-def generate_board(seed_val: int, phrases):
+def generate_board(seed_val: int, phrases: List[str]) -> BoardType:
     """
     Generate a new board using the provided seed value.
     Also resets the clicked_tiles (ensuring the FREE SPACE is clicked) and sets the global today_seed.
+
+    Args:
+        seed_val: Integer used to seed the random generator
+        phrases: List of phrases to use in the board
+
+    Returns:
+        The generated board as a 2D array of phrases
     """
     global board, today_seed, clicked_tiles
 
@@ -61,10 +81,14 @@ def generate_board(seed_val: int, phrases):
     return board
 
 
-def toggle_tile(row, col):
+def toggle_tile(row: int, col: int) -> None:
     """
     Toggle the state of a tile (clicked/unclicked).
     Updates the UI and checks for winner.
+
+    Args:
+        row: Row index of the tile to toggle
+        col: Column index of the tile to toggle
     """
     global clicked_tiles
 
@@ -72,7 +96,7 @@ def toggle_tile(row, col):
     if (row, col) == (2, 2):
         return
 
-    key = (row, col)
+    key: Coordinate = (row, col)
     if key in clicked_tiles:
         clicked_tiles.remove(key)
     else:
@@ -90,18 +114,22 @@ def toggle_tile(row, col):
                 new_card_style = f"background-color: {TILE_UNCLICKED_BG_COLOR}; color: {TILE_UNCLICKED_TEXT_COLOR}; border: none;"
                 new_label_color = TILE_UNCLICKED_TEXT_COLOR
 
-            tile["card"].style(new_card_style)
+            card = cast(ui.card, tile["card"])
+            card.style(new_card_style)
+
             lines = split_phrase_into_lines(phrase)
             line_count = len(lines)
             new_label_style = get_line_style_for_lines(line_count, new_label_color)
 
-            for label_info in tile["labels"]:
-                lbl = label_info["ref"]
-                lbl.classes(label_info["base_classes"])
+            label_list = cast(List[TileLabelInfo], tile["labels"])
+            for label_info in label_list:
+                lbl = cast(ui.label, label_info["ref"])
+                base_classes = cast(str, label_info["base_classes"])
+                lbl.classes(base_classes)
                 lbl.style(new_label_style)
                 lbl.update()
 
-            tile["card"].update()
+            card.update()
 
         container.update()
 
@@ -119,12 +147,12 @@ def toggle_tile(row, col):
         logging.debug(f"JavaScript execution failed: {e}")
 
 
-def check_winner():
+def check_winner() -> None:
     """
     Check for Bingo win condition and update the UI accordingly.
     """
     global bingo_patterns
-    new_patterns = []
+    new_patterns: List[BingoPattern] = []
 
     # Check rows and columns.
     for i in range(5):
@@ -158,7 +186,9 @@ def check_winner():
             new_patterns.append("four_corners")
 
     # Plus shape: complete center row and center column.
-    plus_cells = {(2, c) for c in range(5)} | {(r, 2) for r in range(5)}
+    plus_cells: Set[Coordinate] = {(2, c) for c in range(5)} | {
+        (r, 2) for r in range(5)
+    }
     if all(cell in clicked_tiles for cell in plus_cells):
         if "plus" not in bingo_patterns:
             new_patterns.append("plus")
@@ -171,7 +201,7 @@ def check_winner():
             new_patterns.append("x_shape")
 
     # Outside edges (perimeter): all border cells clicked.
-    perimeter_cells = (
+    perimeter_cells: Set[Coordinate] = (
         {(0, c) for c in range(5)}
         | {(4, c) for c in range(5)}
         | {(r, 0) for r in range(5)}
@@ -183,15 +213,24 @@ def check_winner():
 
     if new_patterns:
         # Separate new win patterns into standard and special ones.
-        special_set = {"blackout", "four_corners", "plus", "x_shape", "perimeter"}
-        standard_new = [p for p in new_patterns if p not in special_set]
-        special_new = [p for p in new_patterns if p in special_set]
+        special_set: Set[str] = {
+            "blackout",
+            "four_corners",
+            "plus",
+            "x_shape",
+            "perimeter",
+        }
+        standard_new: List[BingoPattern] = [
+            p for p in new_patterns if p not in special_set
+        ]
+        special_new: List[BingoPattern] = [p for p in new_patterns if p in special_set]
 
         # Process standard win conditions (rows, columns, diagonals).
         if standard_new:
             for pattern in standard_new:
                 bingo_patterns.add(pattern)
-            standard_total = sum(1 for p in bingo_patterns if p not in special_set)
+            standard_total: int = sum(1 for p in bingo_patterns if p not in special_set)
+            message: str
             if standard_total == 1:
                 message = "BINGO!"
             elif standard_total == 2:
@@ -210,11 +249,11 @@ def check_winner():
         for sp in special_new:
             bingo_patterns.add(sp)
             # Format the name to title-case and append "Bingo!"
-            sp_message = sp.replace("_", " ").title() + " Bingo!"
+            sp_message: str = sp.replace("_", " ").title() + " Bingo!"
             ui.notify(sp_message, color="blue", duration=5)
 
 
-def reset_board():
+def reset_board() -> None:
     """
     Reset the board by clearing all clicked states, clearing winning patterns,
     and re-adding the FREE SPACE.
@@ -228,9 +267,12 @@ def reset_board():
                 clicked_tiles.add((r, c))
 
 
-def generate_new_board(phrases):
+def generate_new_board(phrases: List[str]) -> None:
     """
     Generate a new board with an incremented iteration seed and update all board views.
+
+    Args:
+        phrases: List of phrases to use for the board
     """
     global board_iteration
     board_iteration += 1
@@ -246,33 +288,38 @@ def generate_new_board(phrases):
         container.update()
 
     # Update the seed label if available
-    if "seed_label" in globals() and seed_label:
+    if seed_label is not None:
         seed_label.set_text(f"Seed: {today_seed}")
         seed_label.update()
 
     reset_board()
 
 
-def close_game():
+def close_game() -> None:
     """
-    Close the game - hide the board and update the header text.
+    Close the game - show closed message instead of the board and update the header text.
     This function is called when the close button is clicked.
     """
     global is_game_closed, header_label
     is_game_closed = True
 
     # Update header text on the current view
-    if header_label:
+    if header_label is not None:
         header_label.set_text(CLOSED_HEADER_TEXT)
         header_label.update()
 
-    # Hide all board views (both home and stream)
+    # Show closed message in board containers
+    from src.config.constants import CLOSED_MESSAGE_COLOR, CLOSED_MESSAGE_TEXT
+    from src.ui.board_builder import build_closed_message
+
+    # Replace board with closed message in all views
     for view_key, (container, tile_buttons_local) in board_views.items():
-        container.style("display: none;")
+        container.clear()
+        build_closed_message(container)
         container.update()
 
     # Modify the controls row to only show the New Board button
-    if controls_row:
+    if controls_row is not None:
         controls_row.clear()
         with controls_row:
             with ui.button("", icon="autorenew", on_click=reopen_game).classes(
@@ -293,7 +340,7 @@ def close_game():
     ui.notify("Game has been closed", color="red", duration=3)
 
 
-def reopen_game():
+def reopen_game() -> None:
     """
     Reopen the game after it has been closed.
     This regenerates a new board and resets the UI.
@@ -304,14 +351,14 @@ def reopen_game():
     is_game_closed = False
 
     # Update header text back to original for the current view
-    if header_label:
+    if header_label is not None:
         header_label.set_text(HEADER_TEXT)
         header_label.update()
 
     # Generate a new board
     from src.utils.file_operations import read_phrases_file
 
-    phrases = read_phrases_file()
+    phrases: List[str] = read_phrases_file()
 
     board_iteration += 1
     generate_board(board_iteration, phrases)
@@ -319,7 +366,7 @@ def reopen_game():
     # Rebuild the controls row with all buttons
     from src.ui.controls import rebuild_controls_row
 
-    if controls_row:
+    if controls_row is not None:
         rebuild_controls_row(controls_row)
 
     # Recreate and show all board views
diff --git a/src/types/__init__.py b/src/types/__init__.py
new file mode 100644
index 0000000..7771ab9
--- /dev/null
+++ b/src/types/__init__.py
@@ -0,0 +1,3 @@
+"""
+Type definitions for the Bingo application.
+"""
diff --git a/src/types/ui_types.py b/src/types/ui_types.py
new file mode 100644
index 0000000..fc2d990
--- /dev/null
+++ b/src/types/ui_types.py
@@ -0,0 +1,21 @@
+"""
+UI Type definitions for the Bingo application.
+"""
+
+from typing import Dict, List, Set, Tuple, Union
+
+from nicegui import ui
+
+# Basic types
+Coordinate = Tuple[int, int]
+BoardType = List[List[str]]
+ClickedTiles = Set[Coordinate]
+BingoPattern = str
+BingoPatterns = Set[BingoPattern]
+
+# UI Element types
+TileLabelInfo = Dict[str, Union[ui.label, str]]
+TileInfo = Dict[str, Union[ui.card, List[TileLabelInfo]]]
+TileButtonsDict = Dict[Coordinate, TileInfo]
+BoardViewTuple = Tuple[ui.element, TileButtonsDict]
+BoardViews = Dict[str, BoardViewTuple]
diff --git a/src/ui/board_builder.py b/src/ui/board_builder.py
index a932188..dfbe569 100644
--- a/src/ui/board_builder.py
+++ b/src/ui/board_builder.py
@@ -2,6 +2,8 @@
 Board builder UI component for the Bingo application.
 """
 
+from typing import Callable, cast
+
 from nicegui import ui
 
 from src.config.constants import (
@@ -9,10 +11,13 @@
     BOARD_TILE_FONT_STYLE,
     BOARD_TILE_FONT_WEIGHT,
     CARD_CLASSES,
+    CLOSED_MESSAGE_COLOR,
+    CLOSED_MESSAGE_TEXT,
     FREE_SPACE_TEXT,
     FREE_SPACE_TEXT_COLOR,
     GRID_CLASSES,
     GRID_CONTAINER_CLASS,
+    HEADER_FONT_FAMILY,
     LABEL_CLASSES,
     LABEL_SMALL_CLASSES,
     TILE_CLICKED_BG_COLOR,
@@ -20,10 +25,49 @@
     TILE_UNCLICKED_BG_COLOR,
     TILE_UNCLICKED_TEXT_COLOR,
 )
+from src.types.ui_types import BoardType, ClickedTiles, Coordinate, TileButtonsDict
 from src.utils.text_processing import get_line_style_for_lines, split_phrase_into_lines
 
 
-def build_board(parent, tile_buttons_dict: dict, on_tile_click, board, clicked_tiles):
+def build_closed_message(parent: ui.element) -> None:
+    """
+    Build a message indicating the game is closed, to be displayed in place of the board.
+
+    Args:
+        parent: The parent UI element to build the message in
+    """
+    import logging
+
+    with parent:
+        with ui.element("div").classes(GRID_CONTAINER_CLASS):
+            with ui.element("div").classes(
+                "flex justify-center items-center h-full w-full"
+            ):
+                ui.label(CLOSED_MESSAGE_TEXT).classes("text-center fit-header").style(
+                    f"font-family: {HEADER_FONT_FAMILY}; color: {CLOSED_MESSAGE_COLOR}; font-size: 6rem;"
+                )
+
+    # Run JavaScript to ensure text is resized properly
+    try:
+        js_code = """
+            setTimeout(function() {
+                if (typeof fitty !== 'undefined') {
+                    fitty('.fit-header', { multiLine: true, minSize: 10, maxSize: 2000 });
+                }
+            }, 50);
+        """
+        ui.run_javascript(js_code)
+    except Exception as e:
+        logging.debug(f"JavaScript execution failed: {e}")
+
+
+def build_board(
+    parent: ui.element,
+    tile_buttons_dict: TileButtonsDict,
+    on_tile_click: Callable[[int, int], None],
+    board: BoardType,
+    clicked_tiles: ClickedTiles,
+) -> TileButtonsDict:
     """
     Build the common Bingo board in the given parent element.
     The resulting tile UI elements are added to tile_buttons_dict.
@@ -34,6 +78,9 @@ def build_board(parent, tile_buttons_dict: dict, on_tile_click, board, clicked_t
         on_tile_click: Callback function when a tile is clicked
         board: 2D array of phrases
         clicked_tiles: Set of (row, col) tuples that are clicked
+
+    Returns:
+        The updated tile_buttons_dict with UI elements
     """
     with parent:
         with ui.element("div").classes(GRID_CONTAINER_CLASS):
@@ -104,7 +151,7 @@ def build_board(parent, tile_buttons_dict: dict, on_tile_click, board, clicked_t
     return tile_buttons_dict
 
 
-def create_board_view(background_color: str, is_global: bool):
+def create_board_view(background_color: str, is_global: bool) -> None:
     """
     Creates a board page view based on the background color and a flag.
     If is_global is True, the board uses global variables (home page)
@@ -151,7 +198,7 @@ def on_phrases_change(phrases):
             generate_new_board(phrases)
 
         # Build the home view with controls
-        tile_buttons = {}  # Start with an empty dictionary.
+        tile_buttons: TileButtonsDict = {}  # Start with an empty dictionary
         build_board(container, tile_buttons, toggle_tile, board, clicked_tiles)
         board_views["home"] = (container, tile_buttons)
 
@@ -168,6 +215,6 @@ def on_phrases_change(phrases):
 
     else:
         # Build the stream view (no controls)
-        local_tile_buttons = {}
+        local_tile_buttons: TileButtonsDict = {}
         build_board(container, local_tile_buttons, toggle_tile, board, clicked_tiles)
         board_views["stream"] = (container, local_tile_buttons)
diff --git a/src/ui/sync.py b/src/ui/sync.py
index cde5be1..87e80cc 100644
--- a/src/ui/sync.py
+++ b/src/ui/sync.py
@@ -24,9 +24,12 @@ def sync_board_state():
                 header_label.set_text(CLOSED_HEADER_TEXT)
                 header_label.update()
 
-            # Hide all board views
+            # Show closed message in all board views
+            from src.ui.board_builder import build_closed_message
+
             for view_key, (container, _) in board_views.items():
-                container.style("display: none;")
+                container.clear()
+                build_closed_message(container)
                 container.update()
 
             # Make sure controls row is showing only the Start New Game button
diff --git a/tests/test_ui_functions.py b/tests/test_ui_functions.py
index ffa0c3c..dafea8d 100644
--- a/tests/test_ui_functions.py
+++ b/tests/test_ui_functions.py
@@ -143,7 +143,8 @@ def test_update_tile_styles(self, mock_run_js):
 
     @patch("src.core.game_logic.ui")
     @patch("src.core.game_logic.header_label")
-    def test_close_game(self, mock_header_label, mock_ui):
+    @patch("src.ui.board_builder.build_closed_message")
+    def test_close_game(self, mock_build_closed_message, mock_header_label, mock_ui):
         """Test closing the game functionality"""
         from src.config.constants import CLOSED_HEADER_TEXT
         from src.core.game_logic import board_views, close_game, is_game_closed
@@ -192,10 +193,10 @@ def test_close_game(self, mock_header_label, mock_ui):
             mock_header_label.set_text.assert_called_once_with(CLOSED_HEADER_TEXT)
             mock_header_label.update.assert_called_once()
 
-            # Verify containers are hidden
-            mock_container1.style.assert_called_once_with("display: none;")
+            # Verify containers are cleared and the closed message is built
+            mock_container1.clear.assert_called_once()
             mock_container1.update.assert_called_once()
-            mock_container2.style.assert_called_once_with("display: none;")
+            mock_container2.clear.assert_called_once()
             mock_container2.update.assert_called_once()
 
             # Note: In the new structure, the controls_row clear might not be called directly
@@ -216,7 +217,10 @@ def test_close_game(self, mock_header_label, mock_ui):
             globals()["is_game_closed"] = original_is_game_closed
 
     @patch("main.ui.run_javascript")
-    def test_sync_board_state_when_game_closed(self, mock_run_js):
+    @patch("main.build_closed_message")
+    def test_sync_board_state_when_game_closed(
+        self, mock_build_closed_message, mock_run_js
+    ):
         """Test sync_board_state behavior when game is closed"""
         import main
 
@@ -251,10 +255,10 @@ def test_sync_board_state_when_game_closed(self, mock_run_js):
         main.header_label.set_text.assert_called_once_with(main.CLOSED_HEADER_TEXT)
         main.header_label.update.assert_called_once()
 
-        # Verify containers are hidden
-        mock_container1.style.assert_called_once_with("display: none;")
+        # Verify containers are cleared and closed message is built
+        mock_container1.clear.assert_called_once()
         mock_container1.update.assert_called_once()
-        mock_container2.style.assert_called_once_with("display: none;")
+        mock_container2.clear.assert_called_once()
         mock_container2.update.assert_called_once()
 
         # Verify controls_row is modified