docusaurus.config.ts

@@ -127,6 +127,12 @@ const config: Config = {
             theme: prismThemes.github,
             darkTheme: prismThemes.dracula,
         },
+        mermaid: {
+            theme: {
+                light: 'default',
+                dark: 'base',
+            },
+        },
     } satisfies Preset.ThemeConfig,
 };
 

src/theme/Mermaid/index.tsx

@@ -0,0 +1,82 @@
+import ErrorBoundary from '@docusaurus/ErrorBoundary';
+import { ErrorBoundaryErrorMessageFallback } from '@docusaurus/theme-common';
+import { useColorMode } from '@docusaurus/theme-common';
+import {
+    MermaidContainerClassName,
+    useMermaidConfig,
+    useMermaidRenderResult,
+} from '@docusaurus/theme-mermaid/client';
+import type { Props } from '@theme/Mermaid';
+import type { RenderResult } from 'mermaid';
+import React, { useRef, useEffect, useMemo, type ReactNode } from 'react';
+
+import styles from './styles.module.css';
+
+const NORD_THEME_VARIABLES = {
+    background: '#2e3440',
+    mainBkg: '#3b4252',
+    primaryColor: '#5e81ac',
+    primaryTextColor: '#eceff4',
+    primaryBorderColor: '#88c0d0',
+    secondaryColor: '#434c5e',
+    secondaryTextColor: '#d8dee9',
+    secondaryBorderColor: '#4c566a',
+    tertiaryColor: '#3b4252',
+    tertiaryTextColor: '#d8dee9',
+    tertiaryBorderColor: '#4c566a',
+    lineColor: '#88c0d0',
+    edgeLabelBackground: '#434c5e',
+    textColor: '#eceff4',
+    titleColor: '#88c0d0',
+    nodeBorder: '#4c566a',
+    clusterBkg: '#434c5e',
+    clusterBorder: '#4c566a',
+};
+
+function MermaidRenderResult({ renderResult }: { renderResult: RenderResult }): ReactNode {
+    const ref = useRef<HTMLDivElement>(null);
+
+    useEffect(() => {
+        const div = ref.current!;
+
+        renderResult.bindFunctions?.(div);
+    }, [renderResult]);
+
+    return (
+        <div
+            ref={ref}
+            className={`${MermaidContainerClassName} ${styles.container}`}
+            // eslint-disable-next-line react/no-danger -- mermaid renders trusted SVG
+            dangerouslySetInnerHTML={{ __html: renderResult.svg }}
+        />
+    );
+}
+
+function MermaidRenderer({ value }: Props): ReactNode {
+    const { colorMode } = useColorMode();
+    const baseConfig = useMermaidConfig();
+
+    const config = useMemo(
+        () =>
+            colorMode === 'dark'
+                ? { ...baseConfig, themeVariables: NORD_THEME_VARIABLES }
+                : baseConfig,
+        [colorMode, baseConfig],
+    );
+
+    const renderResult = useMermaidRenderResult({ text: value, config });
+
+    if (renderResult === null) {
+        return null;
+    }
+
+    return <MermaidRenderResult renderResult={renderResult} />;
+}
+
+export default function Mermaid(props: Props): ReactNode {
+    return (
+        <ErrorBoundary fallback={(params) => <ErrorBoundaryErrorMessageFallback {...params} />}>
+            <MermaidRenderer {...props} />
+        </ErrorBoundary>
+    );
+}

src/theme/Mermaid/styles.module.css

@@ -0,0 +1,7 @@
+.container {
+    max-width: 100%;
+}
+
+.container > svg {
+    max-width: 100%;
+}