Move default padding inside iframe

This allows things like the focus ring to not get cut off.

docs/CodeExample.js

@@ -35,7 +35,7 @@ export default function CodeExample(props) {
     return (
       <LiveProvider {...liveProps}>
         <BorderBox {...rest}>
-          <BorderBox bg="white" p={3} border={0} borderBottom={1} borderRadius={0}>
+          <BorderBox bg="white" border={0} borderBottom={1} borderRadius={0}>
             <Frame>
               <LivePreview />
             </Frame>

docs/Frame.js

@@ -41,7 +41,7 @@ export default class Frame extends React.Component {
     return (
       <Measure bounds onResize={rect => this.setHeight(rect.bounds.height)}>
         {({measureRef}) => (
-          <div ref={measureRef} style={{overflow: 'auto'}}>
+          <div ref={measureRef} class="p-3 overflow-auto">
             {children}
           </div>
         )}