docs: fix defaultTheme.colors.green is undefined (#788)

reference issue #786
reference [default tailwind config](https://github.com/tailwindlabs/tailwindcss/blob/master/stubs/config.full.js)

docs/content/2.tailwind/1.config.md

@@ -51,13 +51,13 @@ This config has the highest priority to overwrite the defaults and [tailwindcss.
 
 ::code-group
 ```js [tailwind.config.js]
-import defaultTheme from 'tailwindcss/defaultTheme'
+import colors from 'tailwindcss/colors'
 
 export default {
   theme: {
     extend: {
       colors: {
-        primary: defaultTheme.colors.green
+        primary: colors.green
       }
     }
   }
@@ -66,27 +66,27 @@ export default {
 
 ```ts [tailwind.config.ts]
 import type { Config } from 'tailwindcss'
-import defaultTheme from 'tailwindcss/defaultTheme'
+import colors from 'tailwindcss/colors'
 
 export default <Partial<Config>>{
 	theme: {
     extend: {
       colors: {
-        primary: defaultTheme.colors.green
+        primary: colors.green
       }
     }
   }
 }
 ```
 
 ```js [tailwind.config.cjs]
-const defaultTheme = require('tailwindcss/defaultTheme')
+const colors = require('tailwindcss/colors')
 
 module.exports = {
   theme: {
     extend: {
       colors: {
-        primary: defaultTheme.colors.green
+        primary: colors.green
       }
     }
   }