[Box] Use the default theme (#15019)

packages/material-ui/src/Box/Box.js

@@ -9,7 +9,7 @@ import sizing from '@material-ui/system/sizing';
 import spacing from '@material-ui/system/spacing';
 import typography from '@material-ui/system/typography';
 import css from '@material-ui/system/css';
-import { styled } from '@material-ui/styles';
+import styled from '../styles/styled';
 
 export const styleFunction = css(
   compose(

packages/material-ui/src/Box/Box.test.js

@@ -0,0 +1,29 @@
+import React from 'react';
+import { assert } from 'chai';
+import { createMount } from '@material-ui/core/test-utils';
+import Box from './Box';
+
+describe('<Box />', () => {
+  let mount;
+
+  before(() => {
+    mount = createMount();
+  });
+
+  after(() => {
+    mount.cleanUp();
+  });
+
+  const testChildren = <div className="unique">Hello World</div>;
+
+  it('renders children and box content', () => {
+    const wrapper = mount(
+      <Box component="span" m={1}>
+        {testChildren}
+      </Box>,
+    );
+
+    assert.strictEqual(wrapper.contains(testChildren), true);
+    assert.strictEqual(wrapper.find('span').length, 1);
+  });
+});