docs: display all less variables (#7604)

src/tree-select/README.md

@@ -168,3 +168,18 @@ In every tree object, `text` property defines `id` stands for the unique key whi
   },
 ];
 ```
+
+### Less Variables
+
+How to use: [Custom Theme](#/en-US/theme).
+
+| Name                                  | Default Value       | Description |
+| ------------------------------------- | ------------------- | ----------- |
+| @tree-select-font-size                | `@font-size-md`     | -           |
+| @tree-select-nav-background-color     | `@background-color` | -           |
+| @tree-select-content-background-color | `@white`            | -           |
+| @tree-select-nav-item-padding         | `14px @padding-sm`  | -           |
+| @tree-select-item-height              | `48px`              | -           |
+| @tree-select-item-active-color        | `@red`              | -           |
+| @tree-select-item-disabled-color      | `@gray-5`           | -           |
+| @tree-select-item-selected-size       | `16px`              | -           |

src/tree-select/README.zh-CN.md

@@ -174,3 +174,18 @@ export default {
   },
 ];
 ```
+
+### 样式变量
+
+组件提供了下列 Less 变量，可用于自定义样式，使用方法请参考[主题定制](#/zh-CN/theme)。
+
+| 名称                                  | 默认值              | 描述 |
+| ------------------------------------- | ------------------- | ---- |
+| @tree-select-font-size                | `@font-size-md`     | -    |
+| @tree-select-nav-background-color     | `@background-color` | -    |
+| @tree-select-content-background-color | `@white`            | -    |
+| @tree-select-nav-item-padding         | `14px @padding-sm`  | -    |
+| @tree-select-item-height              | `48px`              | -    |
+| @tree-select-item-active-color        | `@red`              | -    |
+| @tree-select-item-disabled-color      | `@gray-5`           | -    |
+| @tree-select-item-selected-size       | `16px`              | -    |