style: set bg color white when desktop browser

web/src/App.js

@@ -1,5 +1,5 @@
 import React from 'react'
-import styled from 'styled-components'
+import styled, { createGlobalStyle } from 'styled-components'
 
 import { useDeferredState } from './hooks/state'
 import { mobile } from './util/css'
@@ -26,6 +26,8 @@ export default function App() {
   }
 
   return (
+    <>
+      <GlobalStyle />
       <Content>
         <Header>
           <InputContainer>
@@ -54,9 +56,20 @@ export default function App() {
         ) : null}
         <Footer />
       </Content>
+    </>
   )
 }
 
+const GlobalStyle = createGlobalStyle`
+body {
+  background: #ffffff;
+
+  ${mobile} {
+    background: #f5f5f5;
+  }
+}
+`
+
 const Content = styled.div``
 
 const Header = styled.header`
@@ -89,6 +102,10 @@ const Logo = styled.div`
   font-weight: bold;
   font-size: 20px;
   color: #4a90e2;
+
+  ${mobile} {
+    font-size: 15px;
+  }
 `
 
 const Input = styled.input.attrs({

web/src/index.css

@@ -11,7 +11,6 @@ body {
     sans-serif;
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
-  background: #f5f5f5;
 }
 
 code {