Use HorizontalGutter component, simplify Flex

src/core/client/ui/components/TextField/TextField.mdx

@@ -5,16 +5,16 @@ menu: UI Kit
 
 import { Playground, PropsTable } from 'docz'
 import TextField from './TextField.tsx'
-import Flex from '../Flex'
+import HorizontalGutter from '../HorizontalGutter'
 
 # TextField
 
 ## Basic Use
 <Playground>
-  <Flex itemGutter direction="column">
+  <HorizontalGutter>
     <TextField placeholder="This is a placeholder" />
     <TextField defaultValue="This is an input field" />
     <TextField color="error" defaultValue="A TextField with an error" />
     <TextField color="error" defaultValue="A TextField with an error" fullWidth/>
-  </Flex>
+  </HorizontalGutter>
 </Playground>