diff --git a/packages/mermaid/src/rendering-util/createText.ts b/packages/mermaid/src/rendering-util/createText.ts
index 7dab485b4..cc189e46e 100644
--- a/packages/mermaid/src/rendering-util/createText.ts
+++ b/packages/mermaid/src/rendering-util/createText.ts
@@ -204,7 +204,7 @@ export const createText = async (
     width = 200,
     addSvgBackground = false,
   } = {},
-  config: MermaidConfig
+  config?: MermaidConfig
 ) => {
   log.debug(
     'XYZ createText',
diff --git a/packages/mermaid/src/rendering-util/rendering-elements/shapes/util.js b/packages/mermaid/src/rendering-util/rendering-elements/shapes/util.ts
similarity index 66%
rename from packages/mermaid/src/rendering-util/rendering-elements/shapes/util.js
rename to packages/mermaid/src/rendering-util/rendering-elements/shapes/util.ts
index eda1aa9af..fcae715d8 100644
--- a/packages/mermaid/src/rendering-util/rendering-elements/shapes/util.js
+++ b/packages/mermaid/src/rendering-util/rendering-elements/shapes/util.ts
@@ -1,12 +1,18 @@
 import { createText } from '../../createText.js';
+import type { Node } from '../../types.js';
 import { getConfig } from '../../../diagram-api/diagramAPI.js';
 import { select } from 'd3';
 import { evaluate, sanitizeText } from '../../../diagrams/common/common.js';
-import { decodeEntities } from '../../../utils.js';
+import { decodeEntities, handleUndefinedAttr } from '../../../utils.js';
+import type { D3Selection, Point } from '../../../types.js';
 
-export const labelHelper = async (parent, node, _classes) => {
+export const labelHelper = async <T extends SVGGraphicsElement>(
+  parent: D3Selection<T>,
+  node: Node,
+  _classes?: string
+) => {
   let cssClasses;
-  const useHtmlLabels = node.useHtmlLabels || evaluate(getConfig().flowchart.htmlLabels);
+  const useHtmlLabels = node.useHtmlLabels || evaluate(getConfig()?.flowchart?.htmlLabels);
   if (!_classes) {
     cssClasses = 'node default';
   } else {
@@ -20,7 +26,10 @@ export const labelHelper = async (parent, node, _classes) => {
     .attr('id', node.domId || node.id);
 
   // Create the label and insert it after the rect
-  const labelEl = shapeSvg.insert('g').attr('class', 'label').attr('style', node.labelStyle);
+  const labelEl = shapeSvg
+    .insert('g')
+    .attr('class', 'label')
+    .attr('style', handleUndefinedAttr(node.labelStyle));
 
   // Replace label with default value if undefined
   let label;
@@ -30,19 +39,19 @@ export const labelHelper = async (parent, node, _classes) => {
     label = typeof node.label === 'string' ? node.label : node.label[0];
   }
 
-  let text;
-  text = await createText(labelEl, sanitizeText(decodeEntities(label), getConfig()), {
+  const text = await createText(labelEl, sanitizeText(decodeEntities(label), getConfig()), {
     useHtmlLabels,
-    width: node.width || getConfig().flowchart.wrappingWidth,
+    width: node.width || getConfig().flowchart?.wrappingWidth,
+    // @ts-expect-error -- This is currently not used. Should this be `classes` instead?
     cssClasses: 'markdown-node-label',
     style: node.labelStyle,
     addSvgBackground: !!node.icon || !!node.img,
   });
   // Get the size of the label
   let bbox = text.getBBox();
-  const halfPadding = node.padding / 2;
+  const halfPadding = (node?.padding ?? 0) / 2;
 
-  if (evaluate(getConfig().flowchart.htmlLabels)) {
+  if (evaluate(getConfig().flowchart?.htmlLabels)) {
     const div = text.children[0];
     const dv = select(text);
 
@@ -68,7 +77,11 @@ export const labelHelper = async (parent, node, _classes) => {
                     ? getConfig().fontSize
                     : window.getComputedStyle(document.body).fontSize;
                   const enlargingFactor = 5;
-                  const width = parseInt(bodyFontSize, 10) * enlargingFactor + 'px';
+                  const parsedBodyFontSize =
+                    typeof bodyFontSize === 'number'
+                      ? bodyFontSize
+                      : parseInt(bodyFontSize ?? '', 10);
+                  const width = parsedBodyFontSize * enlargingFactor + 'px';
                   img.style.minWidth = width;
                   img.style.maxWidth = width;
                 } else {
@@ -106,19 +119,28 @@ export const labelHelper = async (parent, node, _classes) => {
   return { shapeSvg, bbox, halfPadding, label: labelEl };
 };
 
-export const updateNodeBounds = (node, element) => {
-  const bbox = element.node().getBBox();
+export const updateNodeBounds = <T extends SVGGraphicsElement>(
+  node: Node,
+  // D3Selection<SVGGElement> is for the roughjs case, D3Selection<T> is for the non-roughjs case
+  element: D3Selection<SVGGElement> | D3Selection<T>
+) => {
+  const bbox = element.node()!.getBBox();
   node.width = bbox.width;
   node.height = bbox.height;
 };
 
 /**
- * @param parent
- * @param w
- * @param h
- * @param points
+ * @param parent - Parent element to append the polygon to
+ * @param w - Width of the polygon
+ * @param h - Height of the polygon
+ * @param points - Array of points to create the polygon
  */
-export function insertPolygonShape(parent, w, h, points) {
+export function insertPolygonShape(
+  parent: D3Selection<SVGGElement>,
+  w: number,
+  h: number,
+  points: Point[]
+) {
   return parent
     .insert('polygon', ':first-child')
     .attr(
@@ -133,16 +155,23 @@ export function insertPolygonShape(parent, w, h, points) {
     .attr('transform', 'translate(' + -w / 2 + ',' + h / 2 + ')');
 }
 
-export const getNodeClasses = (node, extra) =>
+export const getNodeClasses = (node: Node, extra?: string) =>
   (node.look === 'handDrawn' ? 'rough-node' : 'node') + ' ' + node.cssClasses + ' ' + (extra || '');
 
-export function createPathFromPoints(points) {
+export function createPathFromPoints(points: Point[]) {
   const pointStrings = points.map((p, i) => `${i === 0 ? 'M' : 'L'}${p.x},${p.y}`);
   pointStrings.push('Z');
   return pointStrings.join(' ');
 }
 
-export function generateFullSineWavePoints(x1, y1, x2, y2, amplitude, numCycles) {
+export function generateFullSineWavePoints(
+  x1: number,
+  y1: number,
+  x2: number,
+  y2: number,
+  amplitude: number,
+  numCycles: number
+) {
   const points = [];
   const steps = 50; // Number of segments to create a smooth curve
   const deltaX = x2 - x1;
@@ -164,13 +193,21 @@ export function generateFullSineWavePoints(x1, y1, x2, y2, amplitude, numCycles)
   return points;
 }
 
+/**
+ * @param centerX - x-coordinate of center of circle
+ * @param centerY - y-coordinate of center of circle
+ * @param radius - radius of circle
+ * @param numPoints - total points required
+ * @param startAngle - angle where arc will start
+ * @param endAngle - angle where arc will end
+ */
 export function generateCirclePoints(
-  centerX, // x-coordinate of center of circle
-  centerY, // x-coordinate of center of circle
-  radius, // radius of circle
-  numPoints, // total points required
-  startAngle, //  angle where arc will start
-  endAngle // angle where arc will end
+  centerX: number,
+  centerY: number,
+  radius: number,
+  numPoints: number,
+  startAngle: number,
+  endAngle: number
 ) {
   const points = [];