diff --git a/CHANGELOG.md b/CHANGELOG.md
index b725c50..5cf9b47 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Update type definition to add `cssNesting` constructor option ([#401](https://github.com/marp-team/marpit/pull/401))
+
 ## v3.1.0 - 2024-08-30
 
 ### Added
diff --git a/index.d.ts b/index.d.ts
index f5898db..03bc242 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -10,6 +10,7 @@ declare namespace Marpit {
     anchor?: boolean | AnchorCallback
     container?: false | Element | Element[]
     cssContainerQuery?: boolean | string | string[]
+    cssNesting?: boolean
     headingDivider?: false | HeadingDivider | HeadingDivider[]
     lang?: string
     looseYAML?: boolean
@@ -47,15 +48,20 @@ declare namespace Marpit {
     ...params: P
   ) => void
 
+  type ThemeMetaType = {
+    [key: string]: StringConstructor | ArrayConstructor
+  }
+
   type ThemeReservedMeta = {
     theme: string
   }
 
-  type ThemeMetaType = {
-    [key: string]: StringConstructor | ArrayConstructor
+  interface ThemeSetOptions {
+    cssNesting?: boolean
   }
 
   type ThemeOptions = {
+    cssNesting?: boolean
     metaType?: ThemeMetaType
   }
 
@@ -126,8 +132,9 @@ declare namespace Marpit {
   }
 
   export class ThemeSet {
-    constructor()
+    constructor(opts?: ThemeSetOptions)
 
+    cssNesting: boolean
     default: Theme | undefined
     metaType: ThemeMetaType