[Doc] translate theme & demo pages (#320)

* fix: Tabbar icon line-height

* [new feature] progress add showPivot prop

* [new feature] TabItem support vue-router

* [new feature] update document header style

* [Doc] add toast english ducoment

* [bugfix] Search box-sizing wrong

* [Doc] update vant-demo respo

* [Doc] translate theme & demo pages

docs/markdown/en-US/theme.md

@@ -1,20 +1,20 @@
-## Custom Theme (In translation)
+## Custom Theme
 
 `Vant` provides a set of default themes, if you want to custom the theme color or other styles, you can use the following methods:
 
-### 方案一. PostCSS 插件
-在项目中直接引入组件对应的 postcss 源代码，并通过 postcss 插件 [postcss-theme-variables](https://www.npmjs.com/package/postcss-theme-variables) 替换颜色变量，步骤如下：
+### Option 1. PostCSS Plugin
+You can import the postcss source code in your own project, then use [postcss-theme-variables](https://www.npmjs.com/package/postcss-theme-variables) to replace the postcss variable.
 
 ```javascript
-// 引入基础样式
+// import base style
 import 'vant/packages/vant-css/src/base.css';
 
-// 引入组价对应的样式
+// import component style
 import 'vant/packages/vant-css/src/button.css';
 import 'vant/packages/vant-css/src/checkbox.css';
 ```
 
-接着在 postcss.config.js 中引入所需的 postcss 插件，并根据项目需求配置颜色变量，所有可用的颜色变量请参考 [配置文件](https://github.com/youzan/vant/blob/dev/packages/vant-css/src/common/var.css)
+Then require the plugin in the postcss.config.js, and configure the variables according to project needs, you can view all the available variables in [profile](https://github.com/youzan/vant/blob/dev/packages/vant-css/src/common/var.css).
 
 ```javascript
 module.exports = {
@@ -39,17 +39,16 @@ module.exports = {
 };
 ```
 
-### 方案二. 本地构建
-可以通过在本地构建 vant-css 的方式生成所需的主题
+### Option 2. Local build
+Vant also support local build to custom themes.
 
 ```bash
-# 克隆仓库
+# Clone the repository
 git clone git@github.com:youzan/vant.git
 cd packages/vant-css
 ```
 
-在本地 vant-css 仓库中，修改 src/common/var.css 中的颜色变量，然后执行以下构建命令，即可生成对应的样式文件
+In the local vant-css repository, modify the variables in src/common/var.css, then execute the following build command to generate the style file.
 ```bash
 npm run build
 ```
-

docs/markdown/zh-CN/theme.md

@@ -9,7 +9,7 @@
 // 引入基础样式
 import 'vant/packages/vant-css/src/base.css';
 
-// 引入组价对应的样式
+// 引入组件对应的样式
 import 'vant/packages/vant-css/src/button.css';
 import 'vant/packages/vant-css/src/checkbox.css';
 ```