feat(FormGroup): add size prop and theme options (#391)

Co-authored-by: Benjamin Canac <canacb1@gmail.com>

docs/content/3.forms/9.form-group.md

@@ -134,6 +134,32 @@ You can also use the `error` prop as a boolean to mark the form element as inval
   The `error` prop will automatically set the `color` prop of the form element to `red`.
 ::
 
+### Size
+
+Use the `size` prop to change the size of the label and the form element.
+
+::component-card
+---
+props:
+  size: 'xl'
+  label: 'Email'
+  hint: 'Optional'
+  description: "We'll only use this for spam."
+  help: 'We will never share your email with anyone else.'
+excludedProps:
+  - label
+  - hint
+  - description
+  - help
+code: >-
+
+  <UInput placeholder="you@example.com" icon="i-heroicons-envelope" />
+---
+
+#default
+:u-input{placeholder="you@example.com" icon="i-heroicons-envelope"}
+::
+
 ## Props
 
 :component-props