diff --git a/integrations/cli/config.test.ts b/integrations/cli/config.test.ts
index 2780e9aca..54ca8c0ca 100644
--- a/integrations/cli/config.test.ts
+++ b/integrations/cli/config.test.ts
@@ -83,3 +83,109 @@ test(
     ])
   },
 )
+
+test(
+  'Config files (CJS, watch mode)',
+  {
+    fs: {
+      'package.json': json`
+        {
+          "dependencies": {
+            "tailwindcss": "workspace:^",
+            "@tailwindcss/cli": "workspace:^"
+          }
+        }
+      `,
+      'index.html': html`
+        <div class="text-primary"></div>
+      `,
+      'tailwind.config.js': js`
+        const myColor = require('./my-color')
+        module.exports = {
+          theme: {
+            extend: {
+              colors: {
+                primary: myColor,
+              },
+            },
+          },
+        }
+      `,
+      'my-color.js': js`module.exports = 'blue'`,
+      'src/index.css': css`
+        @import 'tailwindcss';
+        @config '../tailwind.config.js';
+      `,
+    },
+  },
+  async ({ fs, spawn }) => {
+    await spawn('pnpm tailwindcss --input src/index.css --output dist/out.css --watch')
+
+    await fs.expectFileToContain('dist/out.css', [
+      //
+      candidate`text-primary`,
+      'color: blue',
+    ])
+
+    await fs.write('my-color.js', js`module.exports = 'red'`)
+
+    await fs.expectFileToContain('dist/out.css', [
+      //
+      candidate`text-primary`,
+      'color: red',
+    ])
+  },
+)
+
+test(
+  'Config files (MJS, watch mode)',
+  {
+    fs: {
+      'package.json': json`
+        {
+          "dependencies": {
+            "tailwindcss": "workspace:^",
+            "@tailwindcss/cli": "workspace:^"
+          }
+        }
+      `,
+      'index.html': html`
+        <div class="text-primary"></div>
+      `,
+      'tailwind.config.mjs': js`
+        import myColor from './my-color.mjs'
+        export default {
+          theme: {
+            extend: {
+              colors: {
+                primary: myColor,
+              },
+            },
+          },
+        }
+      `,
+      'my-color.mjs': js`export default 'blue'`,
+      'src/index.css': css`
+        @import 'tailwindcss';
+        @config '../tailwind.config.mjs';
+      `,
+    },
+  },
+  async ({ fs, spawn }) => {
+    await spawn('pnpm tailwindcss --input src/index.css --output dist/out.css --watch')
+
+    await fs.expectFileToContain('dist/out.css', [
+      //
+      candidate`text-primary`,
+      'color: blue',
+    ])
+
+    await fs.write('my-color.mjs', js`export default 'red'`)
+
+    await fs.expectFileToContain('dist/out.css', [
+      //
+      candidate`text-primary`,
+      'color: red',
+    ])
+  },
+)
diff --git a/packages/@tailwindcss-cli/hook/esm.hook.mjs b/packages/@tailwindcss-cli/hook/esm.hook.mjs
index 6f693b817..bde8538b0 100644
--- a/packages/@tailwindcss-cli/hook/esm.hook.mjs
+++ b/packages/@tailwindcss-cli/hook/esm.hook.mjs
@@ -1,3 +1,3 @@
 import { register } from 'node:module'
 
-register(import.meta.resolve('./esm.loader.mjs'))
+register(import.meta.resolve('@tailwindcss/cli/esm-loader'))
diff --git a/packages/@tailwindcss-cli/hook/esm.loader.mjs b/packages/@tailwindcss-cli/hook/esm.loader.mjs
index b21920a52..b7508c778 100644
--- a/packages/@tailwindcss-cli/hook/esm.loader.mjs
+++ b/packages/@tailwindcss-cli/hook/esm.loader.mjs
@@ -13,9 +13,10 @@ export async function resolve(specifier, context, nextResolve) {
   if (id === null) return result
 
   let url = new URL(result.url)
-
   url.searchParams.set('id', id)
 
+  console.log({ url })
+
   return {
     ...result,
     url: `${url}`,
diff --git a/packages/@tailwindcss-cli/hook/require-cache.cjs b/packages/@tailwindcss-cli/hook/require-cache.cjs
new file mode 100644
index 000000000..d073d8701
--- /dev/null
+++ b/packages/@tailwindcss-cli/hook/require-cache.cjs
@@ -0,0 +1,5 @@
+module.exports = function clearRequireCache() {
+  for (const key in require.cache) {
+    delete require.cache[key]
+  }
+}
diff --git a/packages/@tailwindcss-cli/package.json b/packages/@tailwindcss-cli/package.json
index 4a5310492..944fdb2ca 100644
--- a/packages/@tailwindcss-cli/package.json
+++ b/packages/@tailwindcss-cli/package.json
@@ -19,10 +19,14 @@
     "tailwindcss": "./dist/index.mjs"
   },
   "exports": {
-    "./package.json": "./package.json"
+    "./package.json": "./package.json",
+    "./esm-hook": "./hook/esm.hook.mjs",
+    "./esm-loader": "./hook/esm.loader.mjs",
+    "./require-cache": "./hook/require-cache.cjs"
   },
   "files": [
-    "dist"
+    "dist",
+    "hook"
   ],
   "publishConfig": {
     "provenance": true,
diff --git a/packages/@tailwindcss-cli/src/commands/build/index.ts b/packages/@tailwindcss-cli/src/commands/build/index.ts
index 84e17ee71..c5db54c46 100644
--- a/packages/@tailwindcss-cli/src/commands/build/index.ts
+++ b/packages/@tailwindcss-cli/src/commands/build/index.ts
@@ -11,6 +11,7 @@ import atImport from 'postcss-import'
 import * as tailwindcss from 'tailwindcss'
 import type { Arg, Result } from '../../utils/args'
 import { Disposables } from '../../utils/disposables'
+import { getModuleDependencies } from '../../utils/get-module-dependencies'
 import {
   eprintln,
   formatDuration,
@@ -22,6 +23,10 @@ import {
 import { resolveCssId } from '../../utils/resolve'
 import { drainStdin, outputFile } from './utils'
 
+import '@tailwindcss/cli/esm-hook'
+// @ts-ignore
+import clearRequireCache from '@tailwindcss/cli/require-cache'
+
 const css = String.raw
 
 export function options() {
@@ -128,27 +133,35 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
 
   let inputFile = args['--input'] && args['--input'] !== '-' ? args['--input'] : process.cwd()
   let inputBasePath = path.dirname(path.resolve(inputFile))
+  let fullRebuildPaths = [...cssImportPaths]
 
   function compile(css: string) {
     return tailwindcss.compile(css, {
       loadPlugin: async (pluginPath) => {
-        if (pluginPath[0] === '.') {
-          return import(pathToFileURL(path.resolve(inputBasePath, pluginPath)).href).then(
-            (m) => m.default ?? m,
-          )
+        if (pluginPath[0] !== '.') {
+          return import(pluginPath).then((m) => m.default ?? m)
         }
 
-        return import(pluginPath).then((m) => m.default ?? m)
+        let resolvedPath = path.resolve(inputBasePath, pluginPath)
+        fullRebuildPaths.push(resolvedPath)
+        fullRebuildPaths.push(...getModuleDependencies(resolvedPath))
+        return import(pathToFileURL(resolvedPath).href + '?id=' + Date.now()).then(
+          (m) => m.default ?? m,
+        )
       },
 
       loadConfig: async (configPath) => {
-        if (configPath[0] === '.') {
-          return import(pathToFileURL(path.resolve(inputBasePath, configPath)).href).then(
-            (m) => m.default ?? m,
-          )
+        if (configPath[0] !== '.') {
+          return import(configPath).then((m) => m.default ?? m)
         }
 
-        return import(configPath).then((m) => m.default ?? m)
+        console.log('RELOAD')
+        let resolvedPath = path.resolve(inputBasePath, configPath)
+        fullRebuildPaths.push(resolvedPath)
+        fullRebuildPaths.push(...getModuleDependencies(resolvedPath))
+        return import(pathToFileURL(resolvedPath).href + '?id=' + Date.now()).then(
+          (m) => m.default ?? m,
+        )
       },
     })
   }
@@ -177,9 +190,11 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
           let rebuildStrategy: 'incremental' | 'full' = 'incremental'
 
           for (let file of files) {
-            // If one of the changed files is related to the input CSS files, then
-            // we need to do a full rebuild because the theme might have changed.
-            if (cssImportPaths.includes(file)) {
+            // If one of the changed files is related to the input CSS or JS
+            // config/plugin files, then we need to do a full rebuild because
+            // the theme might have changed.
+            if (fullRebuildPaths.includes(file)) {
+              console.log('#############')
               rebuildStrategy = 'full'
 
               // No need to check the rest of the events, because we already know we
@@ -214,6 +229,8 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
                   `,
               args['--input'] ?? base,
             )
+            fullRebuildPaths = cssImportPaths
+            clearRequireCache()
 
             // Create a new compiler, given the new `input`
             compiler = await compile(input)
diff --git a/packages/@tailwindcss-cli/src/utils/get-module-dependencies.ts b/packages/@tailwindcss-cli/src/utils/get-module-dependencies.ts
new file mode 100644
index 000000000..592306641
--- /dev/null
+++ b/packages/@tailwindcss-cli/src/utils/get-module-dependencies.ts
@@ -0,0 +1,85 @@
+import fs from 'fs'
+import path from 'path'
+
+let jsExtensions = ['.js', '.cjs', '.mjs']
+
+// Given the current file `a.ts`, we want to make sure that when importing `b` that we resolve
+// `b.ts` before `b.js`
+//
+// E.g.:
+//
+// a.ts
+//   b // .ts
+//   c // .ts
+// a.js
+//   b // .js or .ts
+
+let jsResolutionOrder = ['', '.js', '.cjs', '.mjs', '.ts', '.cts', '.mts', '.jsx', '.tsx']
+let tsResolutionOrder = ['', '.ts', '.cts', '.mts', '.tsx', '.js', '.cjs', '.mjs', '.jsx']
+
+function resolveWithExtension(file: string, extensions: string[]) {
+  // Try to find `./a.ts`, `./a.cts`, ... from `./a`
+  for (let ext of extensions) {
+    let full = `${file}${ext}`
+    if (fs.existsSync(full) && fs.statSync(full).isFile()) {
+      return full
+    }
+  }
+
+  // Try to find `./a/index.js` from `./a`
+  for (let ext of extensions) {
+    let full = `${file}/index${ext}`
+    if (fs.existsSync(full)) {
+      return full
+    }
+  }
+
+  return null
+}
+
+function* _getModuleDependencies(
+  filename: string,
+  base: string,
+  seen: Set<string>,
+  ext = path.extname(filename),
+): Iterable<string> {
+  // Try to find the file
+  let absoluteFile = resolveWithExtension(
+    path.resolve(base, filename),
+    jsExtensions.includes(ext) ? jsResolutionOrder : tsResolutionOrder,
+  )
+  if (absoluteFile === null) return // File doesn't exist
+
+  // Prevent infinite loops when there are circular dependencies
+  if (seen.has(absoluteFile)) return // Already seen
+  seen.add(absoluteFile)
+
+  // Mark the file as a dependency
+  yield absoluteFile
+
+  // Resolve new base for new imports/requires
+  base = path.dirname(absoluteFile)
+  ext = path.extname(absoluteFile)
+
+  let contents = fs.readFileSync(absoluteFile, 'utf-8')
+
+  // Find imports/requires
+  for (let match of [
+    ...contents.matchAll(/import[\s\S]*?['"](.{3,}?)['"]/gi),
+    ...contents.matchAll(/import[\s\S]*from[\s\S]*?['"](.{3,}?)['"]/gi),
+    ...contents.matchAll(/export[\s\S]*from[\s\S]*?['"](.{3,}?)['"]/gi),
+    ...contents.matchAll(/require\(['"`](.+)['"`]\)/gi),
+  ]) {
+    // Bail out if it's not a relative file
+    if (!match[1].startsWith('.')) continue
+
+    yield* _getModuleDependencies(match[1], base, seen, ext)
+  }
+}
+
+export function getModuleDependencies(absoluteFilePath: string) {
+  if (absoluteFilePath === null) return new Set<string>()
+  return new Set(
+    _getModuleDependencies(absoluteFilePath, path.dirname(absoluteFilePath), new Set()),
+  )
+}
diff --git a/packages/tailwindcss/src/plugin-api.ts b/packages/tailwindcss/src/plugin-api.ts
index 99324b070..4b74811e0 100644
--- a/packages/tailwindcss/src/plugin-api.ts
+++ b/packages/tailwindcss/src/plugin-api.ts
@@ -366,8 +366,9 @@ export function registerPlugins(
     handler(pluginApi)
   }
 
-  // Theme keys don't need to read from the compat config because core plugins
-  // _already_ look through "fallback" theme keys
+  // Merge the user-configured theme keys into the design system. The compat
+  // config would otherwise expand into namespaces like `background-color` which
+  // core utilities already read from.
   mergeIntoTheme(designSystem, userConfig)
 
   return {