diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5500a5a9..9c3c37a9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Added:
+- Tree Export: Mermaid diagram to include theme.
+### Fixed:
+- Misc: Doctest for docstrings, docstring to indicate usage prefers `node_name` to `name`.
+- Tree Export: Mermaid diagram title to add newline.
 
 ## [0.22.1] - 2024-11-03
 ### Added:
diff --git a/bigtree/node/node.py b/bigtree/node/node.py
index 785fac00..f0a0a874 100644
--- a/bigtree/node/node.py
+++ b/bigtree/node/node.py
@@ -61,7 +61,9 @@ class Node(basenode.BaseNode):
 
     Get `Node` configuration
 
-    1. ``node_name``: Get node name, without accessing `name` directly
+    1. ``node_name``: Get node name, without accessing `name` directly.
+        This is the preferred way to access node name as `node_name` is
+        immutable, whereas `name` is mutable.
     2. ``path_name``: Get path name from root, separated by `sep`
 
     **Node Methods**
diff --git a/bigtree/tree/export.py b/bigtree/tree/export.py
index db505275..baead46c 100644
--- a/bigtree/tree/export.py
+++ b/bigtree/tree/export.py
@@ -1430,6 +1430,7 @@ def get_list_of_text_dimensions(
 def tree_to_mermaid(
     tree: T,
     title: str = "",
+    theme: Optional[str] = None,
     rankdir: str = "TB",
     line_shape: str = "basis",
     node_colour: str = "",
@@ -1447,6 +1448,7 @@ def tree_to_mermaid(
 
     Parameters for customizations that apply to entire flowchart include:
         - Title, `title`
+        - Theme, `theme`
         - Layout direction, `rankdir`
         - Line shape or curvature, `line_shape`
         - Fill colour of nodes, `node_colour`
@@ -1465,6 +1467,13 @@ def tree_to_mermaid(
 
     **Accepted Parameter Values**
 
+    Possible theme:
+        - default
+        - neutral: great for black and white documents
+        - dark: great for dark-mode
+        - forest: shades of geen
+        - base: theme that can be modified, use it for customizations
+
     Possible rankdir:
         - `TB`: top-to-bottom
         - `BT`: bottom-to-top
@@ -1546,6 +1555,7 @@ def tree_to_mermaid(
         >>> graph = tree_to_mermaid(
         ...     root,
         ...     title="Mermaid Diagram",
+        ...     theme="forest",
         ...     node_shape_attr="node_shape",
         ...     edge_label="edge_label",
         ...     edge_arrow_attr="edge_arrow",
@@ -1556,7 +1566,7 @@ def tree_to_mermaid(
         ---
         title: Mermaid Diagram
         ---
-        %%{ init: { 'flowchart': { 'curve': 'basis' } } }%%
+        %%{ init: { 'flowchart': { 'curve': 'basis' }, 'theme': 'forest' } }%%
         flowchart TB
         0{"a"} ==>|Child 1| 0-0("b")
         0-0 --> 0-0-0("d"):::class0-0-0
@@ -1593,12 +1603,15 @@ def tree_to_mermaid(
     """
     from bigtree.tree.helper import clone_tree
 
+    themes = constants.MermaidConstants.THEMES
     rankdirs = constants.MermaidConstants.RANK_DIR
     line_shapes = constants.MermaidConstants.LINE_SHAPES
     node_shapes = constants.MermaidConstants.NODE_SHAPES
     edge_arrows = constants.MermaidConstants.EDGE_ARROWS
 
     # Assertions
+    if theme:
+        assertions.assert_str_in_list("theme", theme, themes)
     assertions.assert_str_in_list("rankdir", rankdir, rankdirs)
     assertions.assert_key_in_dict("node_shape", node_shape, node_shapes)
     assertions.assert_str_in_list("line_shape", line_shape, line_shapes)
@@ -1609,8 +1622,9 @@ def tree_to_mermaid(
     style_template = "classDef {style_name} {style}"
 
     # Content
+    theme_mermaid = f", 'theme': '{theme}'" if theme else ""
     title = f"---\ntitle: {title}\n---\n" if title else ""
-    line_style = f"%%{{ init: {{ 'flowchart': {{ 'curve': '{line_shape}' }} }} }}%%"
+    line_style = f"%%{{ init: {{ 'flowchart': {{ 'curve': '{line_shape}' }}{theme_mermaid} }} }}%%"
     styles = []
     flows = []
 
diff --git a/bigtree/utils/constants.py b/bigtree/utils/constants.py
index 63e099ca..8c46a305 100644
--- a/bigtree/utils/constants.py
+++ b/bigtree/utils/constants.py
@@ -171,6 +171,7 @@ def __post_init__(self) -> None:
 
 
 class MermaidConstants:
+    THEMES: List[str] = ["default", "neutral", "dark", "forest", "base"]
     RANK_DIR: List[str] = ["TB", "BT", "LR", "RL"]
     LINE_SHAPES: List[str] = [
         "basis",
diff --git a/tests/tree/test_export.py b/tests/tree/test_export.py
index 0911f3d4..8d12e1ec 100644
--- a/tests/tree/test_export.py
+++ b/tests/tree/test_export.py
@@ -1653,7 +1653,26 @@ class TestTreeToDot:
     @staticmethod
     def test_tree_to_dot(tree_node):
         graph = export.tree_to_dot(tree_node)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0;\nd0 [label=d];\nb0 -> d0;\ne0 [label=e];\nb0 -> e0;\ng0 [label=g];\ne0 -> g0;\nh0 [label=h];\ne0 -> h0;\nc0 [label=c];\na0 -> c0;\nf0 [label=f];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g];\n"
+            "e0 -> g0;\n"
+            "h0 [label=h];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree.png")
@@ -1665,7 +1684,29 @@ def test_tree_to_dot(tree_node):
     @staticmethod
     def test_tree_to_dot_multiple(tree_node, tree_node_plot):
         graph = export.tree_to_dot([tree_node, tree_node_plot])
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0;\nd0 [label=d];\nb0 -> d0;\ne0 [label=e];\nb0 -> e0;\ng0 [label=g];\ne0 -> g0;\nh0 [label=h];\ne0 -> h0;\nc0 [label=c];\na0 -> c0;\nf0 [label=f];\nc0 -> f0;\nz0 [label=z];\ny0 [label=y];\nz0 -> y0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g];\n"
+            "e0 -> g0;\n"
+            "h0 [label=h];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f];\n"
+            "c0 -> f0;\n"
+            "z0 [label=z];\n"
+            "y0 [label=y];\n"
+            "z0 -> y0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_multiple.png")
@@ -1677,7 +1718,26 @@ def test_tree_to_dot_multiple(tree_node, tree_node_plot):
     @staticmethod
     def test_tree_to_dot_duplicate_names(tree_node_duplicate_names):
         graph = export.tree_to_dot(tree_node_duplicate_names)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\na1 [label=a];\na0 -> a1;\na2 [label=a];\na1 -> a2;\nb0 [label=b];\na1 -> b0;\na3 [label=a];\nb0 -> a3;\nb1 [label=b];\nb0 -> b1;\nb2 [label=b];\na0 -> b2;\na4 [label=a];\nb2 -> a4;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "a1 [label=a];\n"
+            "a0 -> a1;\n"
+            "a2 [label=a];\n"
+            "a1 -> a2;\n"
+            "b0 [label=b];\n"
+            "a1 -> b0;\n"
+            "a3 [label=a];\n"
+            "b0 -> a3;\n"
+            "b1 [label=b];\n"
+            "b0 -> b1;\n"
+            "b2 [label=b];\n"
+            "a0 -> b2;\n"
+            "a4 [label=a];\n"
+            "b2 -> a4;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_duplicate_names.png")
@@ -1695,7 +1755,26 @@ def test_tree_to_dot_type_error(dag_node):
     @staticmethod
     def test_tree_to_dot_directed(tree_node):
         graph = export.tree_to_dot(tree_node, directed=False)
-        expected = """strict graph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -- b0;\nd0 [label=d];\nb0 -- d0;\ne0 [label=e];\nb0 -- e0;\ng0 [label=g];\ne0 -- g0;\nh0 [label=h];\ne0 -- h0;\nc0 [label=c];\na0 -- c0;\nf0 [label=f];\nc0 -- f0;\n}\n"""
+        expected = (
+            "strict graph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -- b0;\n"
+            "d0 [label=d];\n"
+            "b0 -- d0;\n"
+            "e0 [label=e];\n"
+            "b0 -- e0;\n"
+            "g0 [label=g];\n"
+            "e0 -- g0;\n"
+            "h0 [label=h];\n"
+            "e0 -- h0;\n"
+            "c0 [label=c];\n"
+            "a0 -- c0;\n"
+            "f0 [label=f];\n"
+            "c0 -- f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_undirected.png")
@@ -1707,7 +1786,26 @@ def test_tree_to_dot_directed(tree_node):
     @staticmethod
     def test_tree_to_dot_bg_colour(tree_node):
         graph = export.tree_to_dot(tree_node, bg_colour="blue")
-        expected = """strict digraph G {\nbgcolor=blue;\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0;\nd0 [label=d];\nb0 -> d0;\ne0 [label=e];\nb0 -> e0;\ng0 [label=g];\ne0 -> g0;\nh0 [label=h];\ne0 -> h0;\nc0 [label=c];\na0 -> c0;\nf0 [label=f];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "bgcolor=blue;\n"
+            "rankdir=TB;\na0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g];\n"
+            "e0 -> g0;\n"
+            "h0 [label=h];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_bg_colour.png")
@@ -1722,7 +1820,26 @@ def test_tree_to_dot_bg_colour(tree_node):
     )
     def test_tree_to_dot_fill_colour(tree_node):
         graph = export.tree_to_dot(tree_node, node_colour="gold")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [fillcolor=gold, label=a, style=filled];\nb0 [fillcolor=gold, label=b, style=filled];\na0 -> b0;\nd0 [fillcolor=gold, label=d, style=filled];\nb0 -> d0;\ne0 [fillcolor=gold, label=e, style=filled];\nb0 -> e0;\ng0 [fillcolor=gold, label=g, style=filled];\ne0 -> g0;\nh0 [fillcolor=gold, label=h, style=filled];\ne0 -> h0;\nc0 [fillcolor=gold, label=c, style=filled];\na0 -> c0;\nf0 [fillcolor=gold, label=f, style=filled];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [fillcolor=gold, label=a, style=filled];\n"
+            "b0 [fillcolor=gold, label=b, style=filled];\n"
+            "a0 -> b0;\n"
+            "d0 [fillcolor=gold, label=d, style=filled];\n"
+            "b0 -> d0;\n"
+            "e0 [fillcolor=gold, label=e, style=filled];\n"
+            "b0 -> e0;\n"
+            "g0 [fillcolor=gold, label=g, style=filled];\n"
+            "e0 -> g0;\n"
+            "h0 [fillcolor=gold, label=h, style=filled];\n"
+            "e0 -> h0;\n"
+            "c0 [fillcolor=gold, label=c, style=filled];\n"
+            "a0 -> c0;\n"
+            "f0 [fillcolor=gold, label=f, style=filled];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_fill_colour.png")
@@ -1738,7 +1855,26 @@ def test_tree_to_dot_fill_colour(tree_node):
     )
     def test_tree_to_dot_fill_colour2(tree_node):
         graph = export.tree_to_dot(tree_node, node_colour="gold")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a, style=filled, fillcolor=gold];\nb0 [label=b, style=filled, fillcolor=gold];\na0 -> b0;\nd0 [label=d, style=filled, fillcolor=gold];\nb0 -> d0;\ne0 [label=e, style=filled, fillcolor=gold];\nb0 -> e0;\ng0 [label=g, style=filled, fillcolor=gold];\ne0 -> g0;\nh0 [label=h, style=filled, fillcolor=gold];\ne0 -> h0;\nc0 [label=c, style=filled, fillcolor=gold];\na0 -> c0;\nf0 [label=f, style=filled, fillcolor=gold];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a, style=filled, fillcolor=gold];\n"
+            "b0 [label=b, style=filled, fillcolor=gold];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d, style=filled, fillcolor=gold];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e, style=filled, fillcolor=gold];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g, style=filled, fillcolor=gold];\n"
+            "e0 -> g0;\n"
+            "h0 [label=h, style=filled, fillcolor=gold];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c, style=filled, fillcolor=gold];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f, style=filled, fillcolor=gold];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_fill_colour.png")
@@ -1750,7 +1886,26 @@ def test_tree_to_dot_fill_colour2(tree_node):
     @staticmethod
     def test_tree_to_dot_edge_colour(tree_node):
         graph = export.tree_to_dot(tree_node, edge_colour="red")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0  [color=red];\nd0 [label=d];\nb0 -> d0  [color=red];\ne0 [label=e];\nb0 -> e0  [color=red];\ng0 [label=g];\ne0 -> g0  [color=red];\nh0 [label=h];\ne0 -> h0  [color=red];\nc0 [label=c];\na0 -> c0  [color=red];\nf0 [label=f];\nc0 -> f0  [color=red];\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0  [color=red];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0  [color=red];\n"
+            "e0 [label=e];\n"
+            "b0 -> e0  [color=red];\n"
+            "g0 [label=g];\n"
+            "e0 -> g0  [color=red];\n"
+            "h0 [label=h];\n"
+            "e0 -> h0  [color=red];\n"
+            "c0 [label=c];\n"
+            "a0 -> c0  [color=red];\n"
+            "f0 [label=f];\n"
+            "c0 -> f0  [color=red];\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_edge_colour.png")
@@ -1762,7 +1917,22 @@ def test_tree_to_dot_edge_colour(tree_node):
     @staticmethod
     def test_tree_to_dot_node_shape(tree_node):
         graph = export.tree_to_dot(tree_node, node_shape="triangle")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a, shape=triangle];\nb0 [label=b, shape=triangle];\na0 -> b0;\nd0 [label=d, shape=triangle];\nb0 -> d0;\ne0 [label=e, shape=triangle];\nb0 -> e0;\ng0 [label=g, shape=triangle];\ne0 -> g0;\nh0 [label=h, shape=triangle];\ne0 -> h0;\nc0 [label=c, shape=triangle];\na0 -> c0;\nf0 [label=f, shape=triangle];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a, shape=triangle];\nb0 [label=b, shape=triangle];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d, shape=triangle];\n"
+            "b0 -> d0;\ne0 [label=e, shape=triangle];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g, shape=triangle];\n"
+            "e0 -> g0;\nh0 [label=h, shape=triangle];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c, shape=triangle];\n"
+            "a0 -> c0;\nf0 [label=f, shape=triangle];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_node_shape.png")
@@ -1777,7 +1947,25 @@ def test_tree_to_dot_node_shape(tree_node):
     )
     def test_tree_to_dot_node_attr(tree_node_style):
         graph = export.tree_to_dot(tree_node_style, node_attr="node_style")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [fillcolor=gold, label=a, style=filled];\nb0 [fillcolor=blue, label=b, style=filled];\na0 -> b0;\nd0 [fillcolor=green, label=d, style=filled];\nb0 -> d0;\ng0 [fillcolor=red, label=g, style=filled];\nd0 -> g0;\ne0 [fillcolor=green, label=e, style=filled];\nb0 -> e0;\nh0 [fillcolor=red, label=h, style=filled];\ne0 -> h0;\nc0 [fillcolor=blue, label=c, style=filled];\na0 -> c0;\nf0 [fillcolor=green, label=f, style=filled];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [fillcolor=gold, label=a, style=filled];\n"
+            "b0 [fillcolor=blue, label=b, style=filled];\na0 -> b0;\n"
+            "d0 [fillcolor=green, label=d, style=filled];\n"
+            "b0 -> d0;\n"
+            "g0 [fillcolor=red, label=g, style=filled];\n"
+            "d0 -> g0;\n"
+            "e0 [fillcolor=green, label=e, style=filled];\n"
+            "b0 -> e0;\n"
+            "h0 [fillcolor=red, label=h, style=filled];\n"
+            "e0 -> h0;\n"
+            "c0 [fillcolor=blue, label=c, style=filled];\n"
+            "a0 -> c0;\n"
+            "f0 [fillcolor=green, label=f, style=filled];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_node_attr.png")
@@ -1793,7 +1981,26 @@ def test_tree_to_dot_node_attr(tree_node_style):
     )
     def test_tree_to_dot_node_attr2(tree_node_style):
         graph = export.tree_to_dot(tree_node_style, node_attr="node_style")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a, style=filled, fillcolor=gold];\nb0 [label=b, style=filled, fillcolor=blue];\na0 -> b0;\nd0 [label=d, style=filled, fillcolor=green];\nb0 -> d0;\ng0 [label=g, style=filled, fillcolor=red];\nd0 -> g0;\ne0 [label=e, style=filled, fillcolor=green];\nb0 -> e0;\nh0 [label=h, style=filled, fillcolor=red];\ne0 -> h0;\nc0 [label=c, style=filled, fillcolor=blue];\na0 -> c0;\nf0 [label=f, style=filled, fillcolor=green];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a, style=filled, fillcolor=gold];\n"
+            "b0 [label=b, style=filled, fillcolor=blue];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d, style=filled, fillcolor=green];\n"
+            "b0 -> d0;\n"
+            "g0 [label=g, style=filled, fillcolor=red];\n"
+            "d0 -> g0;\n"
+            "e0 [label=e, style=filled, fillcolor=green];\n"
+            "b0 -> e0;\n"
+            "h0 [label=h, style=filled, fillcolor=red];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c, style=filled, fillcolor=blue];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f, style=filled, fillcolor=green];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_node_attr.png")
@@ -1817,7 +2024,26 @@ def get_node_attr(node):
             return {"style": "filled", "fillcolor": "red"}
 
         graph = export.tree_to_dot(tree_node_style_callable, node_attr=get_node_attr)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [fillcolor=gold, label=a, style=filled];\nb0 [fillcolor=blue, label=b, style=filled];\na0 -> b0;\nd0 [fillcolor=green, label=d, style=filled];\nb0 -> d0;\ng0 [fillcolor=red, label=g, style=filled];\nd0 -> g0;\ne0 [fillcolor=green, label=e, style=filled];\nb0 -> e0;\nh0 [fillcolor=red, label=h, style=filled];\ne0 -> h0;\nc0 [fillcolor=blue, label=c, style=filled];\na0 -> c0;\nf0 [fillcolor=green, label=f, style=filled];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [fillcolor=gold, label=a, style=filled];\n"
+            "b0 [fillcolor=blue, label=b, style=filled];\n"
+            "a0 -> b0;\n"
+            "d0 [fillcolor=green, label=d, style=filled];\n"
+            "b0 -> d0;\n"
+            "g0 [fillcolor=red, label=g, style=filled];\n"
+            "d0 -> g0;\n"
+            "e0 [fillcolor=green, label=e, style=filled];\n"
+            "b0 -> e0;\n"
+            "h0 [fillcolor=red, label=h, style=filled];\n"
+            "e0 -> h0;\n"
+            "c0 [fillcolor=blue, label=c, style=filled];\n"
+            "a0 -> c0;\n"
+            "f0 [fillcolor=green, label=f, style=filled];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_node_attr_callable.png")
@@ -1842,7 +2068,26 @@ def get_node_attr(node):
             return {"style": "filled", "fillcolor": "red"}
 
         graph = export.tree_to_dot(tree_node_style_callable, node_attr=get_node_attr)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a, style=filled, fillcolor=gold];\nb0 [label=b, style=filled, fillcolor=blue];\na0 -> b0;\nd0 [label=d, style=filled, fillcolor=green];\nb0 -> d0;\ng0 [label=g, style=filled, fillcolor=red];\nd0 -> g0;\ne0 [label=e, style=filled, fillcolor=green];\nb0 -> e0;\nh0 [label=h, style=filled, fillcolor=red];\ne0 -> h0;\nc0 [label=c, style=filled, fillcolor=red];\na0 -> c0;\nf0 [label=f, style=filled, fillcolor=green];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a, style=filled, fillcolor=gold];\n"
+            "b0 [label=b, style=filled, fillcolor=blue];\n"
+            "a0 -> b0;\n"
+            "d0 [label=d, style=filled, fillcolor=green];\n"
+            "b0 -> d0;\n"
+            "g0 [label=g, style=filled, fillcolor=red];\n"
+            "d0 -> g0;\n"
+            "e0 [label=e, style=filled, fillcolor=green];\n"
+            "b0 -> e0;\n"
+            "h0 [label=h, style=filled, fillcolor=red];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c, style=filled, fillcolor=red];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f, style=filled, fillcolor=green];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_node_attr_callable.png")
@@ -1857,7 +2102,26 @@ def get_node_attr(node):
     )
     def test_tree_to_dot_edge_attr(tree_node_style):
         graph = export.tree_to_dot(tree_node_style, edge_attr="edge_style")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0  [label=b, style=bold];\nd0 [label=d];\nb0 -> d0  [label=1, style=bold];\ng0 [label=g];\nd0 -> g0  [label=4, style=bold];\ne0 [label=e];\nb0 -> e0  [label=2, style=bold];\nh0 [label=h];\ne0 -> h0  [label=5, style=bold];\nc0 [label=c];\na0 -> c0  [label=c, style=bold];\nf0 [label=f];\nc0 -> f0  [label=3, style=bold];\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0  [label=b, style=bold];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0  [label=1, style=bold];\n"
+            "g0 [label=g];\n"
+            "d0 -> g0  [label=4, style=bold];\n"
+            "e0 [label=e];\n"
+            "b0 -> e0  [label=2, style=bold];\n"
+            "h0 [label=h];\n"
+            "e0 -> h0  [label=5, style=bold];\n"
+            "c0 [label=c];\n"
+            "a0 -> c0  [label=c, style=bold];\n"
+            "f0 [label=f];\n"
+            "c0 -> f0  [label=3, style=bold];\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_edge_attr.png")
@@ -1873,7 +2137,26 @@ def test_tree_to_dot_edge_attr(tree_node_style):
     )
     def test_tree_to_dot_edge_attr2(tree_node_style):
         graph = export.tree_to_dot(tree_node_style, edge_attr="edge_style")
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0 [style=bold, label=b];\nd0 [label=d];\nb0 -> d0 [style=bold, label=1];\ng0 [label=g];\nd0 -> g0 [style=bold, label=4];\ne0 [label=e];\nb0 -> e0 [style=bold, label=2];\nh0 [label=h];\ne0 -> h0 [style=bold, label=5];\nc0 [label=c];\na0 -> c0 [style=bold, label=c];\nf0 [label=f];\nc0 -> f0 [style=bold, label=3];\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0 [style=bold, label=b];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0 [style=bold, label=1];\n"
+            "g0 [label=g];\n"
+            "d0 -> g0 [style=bold, label=4];\n"
+            "e0 [label=e];\n"
+            "b0 -> e0 [style=bold, label=2];\n"
+            "h0 [label=h];\n"
+            "e0 -> h0 [style=bold, label=5];\n"
+            "c0 [label=c];\n"
+            "a0 -> c0 [style=bold, label=c];\n"
+            "f0 [label=f];\n"
+            "c0 -> f0 [style=bold, label=3];\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_edge_attr.png")
@@ -1902,7 +2185,26 @@ def get_edge_attr(node):
             raise Exception("Node with invalid edge_attr not covered")
 
         graph = export.tree_to_dot(tree_node_style_callable, edge_attr=get_edge_attr)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0  [label=b, style=bold];\nd0 [label=d];\nb0 -> d0  [label=1, style=bold];\ng0 [label=g];\nd0 -> g0  [label=4, style=bold];\ne0 [label=e];\nb0 -> e0  [label=2, style=bold];\nh0 [label=h];\ne0 -> h0  [label=5, style=bold];\nc0 [label=c];\na0 -> c0  [label=c, style=bold];\nf0 [label=f];\nc0 -> f0  [label=3, style=bold];\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b];\n"
+            "a0 -> b0  [label=b, style=bold];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0  [label=1, style=bold];\n"
+            "g0 [label=g];\n"
+            "d0 -> g0  [label=4, style=bold];\n"
+            "e0 [label=e];\n"
+            "b0 -> e0  [label=2, style=bold];\n"
+            "h0 [label=h];\n"
+            "e0 -> h0  [label=5, style=bold];\n"
+            "c0 [label=c];\n"
+            "a0 -> c0  [label=c, style=bold];\n"
+            "f0 [label=f];\n"
+            "c0 -> f0  [label=3, style=bold];\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_edge_attr_callable.png")
@@ -1932,7 +2234,25 @@ def get_edge_attr(node):
             raise Exception("Node with invalid edge_attr not covered")
 
         graph = export.tree_to_dot(tree_node_style_callable, edge_attr=get_edge_attr)
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b];\na0 -> b0 [style=bold, label=b];\nd0 [label=d];\nb0 -> d0 [style=bold, label=1];\ng0 [label=g];\nd0 -> g0 [style=bold, label=4];\ne0 [label=e];\nb0 -> e0 [style=bold, label=2];\nh0 [label=h];\ne0 -> h0 [style=bold, label=5];\nc0 [label=c];\na0 -> c0 [style=bold, label=c];\nf0 [label=f];\nc0 -> f0 [style=bold, label=3];\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\nb0 [label=b];\n"
+            "a0 -> b0 [style=bold, label=b];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0 [style=bold, label=1];\n"
+            "g0 [label=g];\n"
+            "d0 -> g0 [style=bold, label=4];\n"
+            "e0 [label=e];\n"
+            "b0 -> e0 [style=bold, label=2];\n"
+            "h0 [label=h];\n"
+            "e0 -> h0 [style=bold, label=5];\n"
+            "c0 [label=c];\n"
+            "a0 -> c0 [style=bold, label=c];\n"
+            "f0 [label=f];\n"
+            "c0 -> f0 [style=bold, label=3];\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_edge_attr_callable.png")
@@ -1955,7 +2275,26 @@ def test_tree_to_dot_attr_override(tree_node):
         graph = export.tree_to_dot(
             tree_node, node_attr="node_style", edge_attr="edge_style"
         )
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [fillcolor=blue, label=b, style=filled];\na0 -> b0  [style=bold];\nd0 [label=d];\nb0 -> d0;\ne0 [label=e];\nb0 -> e0;\ng0 [label=g];\ne0 -> g0;\nh0 [label=h];\ne0 -> h0;\nc0 [label=c];\na0 -> c0;\nf0 [label=f];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [fillcolor=blue, label=b, style=filled];\n"
+            "a0 -> b0  [style=bold];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e];\n"
+            "b0 -> e0;\n"
+            "g0 [label=g];\n"
+            "e0 -> g0;\n"
+            "h0 [label=h];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c];\n"
+            "a0 -> c0;\n"
+            "f0 [label=f];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_attr_override.png")
@@ -1979,7 +2318,23 @@ def test_tree_to_dot_attr_override2(tree_node):
         graph = export.tree_to_dot(
             tree_node, node_attr="node_style", edge_attr="edge_style"
         )
-        expected = """strict digraph G {\nrankdir=TB;\na0 [label=a];\nb0 [label=b, style=filled, fillcolor=blue];\na0 -> b0 [style=bold];\nd0 [label=d];\nb0 -> d0;\ne0 [label=e];\nb0 -> e0;\ng0 [label=g];\ne0 -> g0;\nh0 [label=h];\ne0 -> h0;\nc0 [label=c];\na0 -> c0;\nf0 [label=f];\nc0 -> f0;\n}\n"""
+        expected = (
+            "strict digraph G {\n"
+            "rankdir=TB;\n"
+            "a0 [label=a];\n"
+            "b0 [label=b, style=filled, fillcolor=blue];\n"
+            "a0 -> b0 [style=bold];\n"
+            "d0 [label=d];\n"
+            "b0 -> d0;\n"
+            "e0 [label=e];\nb0 -> e0;\n"
+            "g0 [label=g];\n"
+            "e0 -> g0;\nh0 [label=h];\n"
+            "e0 -> h0;\n"
+            "c0 [label=c];\na0 -> c0;\n"
+            "f0 [label=f];\n"
+            "c0 -> f0;\n"
+            "}\n"
+        )
         actual = graph.to_string()
         if LOCAL:
             graph.write_png("tests/tree_attr_override.png")
@@ -2121,6 +2476,33 @@ def test_tree_to_mermaid_title(tree_node):
         )
         assert mermaid_md == expected_str
 
+    @staticmethod
+    def test_tree_to_mermaid_theme(tree_node):
+        mermaid_md = export.tree_to_mermaid(tree_node, theme="forest")
+        expected_str = (
+            """```mermaid\n"""
+            """%%{ init: { \'flowchart\': { \'curve\': \'basis\' }, \'theme\': \'forest\' } }%%\n"""
+            """flowchart TB\n"""
+            """0("a") --> 0-0("b")\n"""
+            """0-0 --> 0-0-0("d")\n"""
+            """0-0 --> 0-0-1("e")\n"""
+            """0-0-1 --> 0-0-1-0("g")\n"""
+            """0-0-1 --> 0-0-1-1("h")\n"""
+            """0("a") --> 0-1("c")\n"""
+            """0-1 --> 0-1-0("f")\n"""
+            """classDef default stroke-width:1\n"""
+            """```"""
+        )
+        assert mermaid_md == expected_str
+
+    @staticmethod
+    def test_tree_to_mermaid_invalid_theme_error(tree_node):
+        with pytest.raises(ValueError) as exc_info:
+            export.tree_to_mermaid(tree_node, theme="invalid")
+        assert str(exc_info.value).startswith(
+            Constants.ERROR_NODE_MERMAID_INVALID_ARGUMENT.format(parameter="theme")
+        )
+
     @staticmethod
     def test_tree_to_mermaid_invalid_rankdir_error(tree_node):
         with pytest.raises(ValueError) as exc_info: