docs: Add FAQ about `@line-height-base` (#39565)

docs/react/faq.en-US.md

@@ -186,6 +186,12 @@ You should only access the API by official doc with ref. Directly access interna
 
 For historical reasons, the display names of the pop components are not uniform, and both `open` and `visible` are used. This makes the memory cost that non-tsx users encounter when developing. It also leads to ambiguity about what name to choose when adding a feature. So we want to unify the attribute name, you can still use the original `visible` and it will still be backward compatible, but we will remove this attribute from the documentation as of v5.
 
+## Setting the style variable '@line-height-base' caused a layout exception.
+
+Because `@line-height-base` is involved in the layout calculation of some components, only `number` units are supported. If `20px` is passed, it will be interpreted as `20 ` for calculation, resulting in a layout exception.
+
+Related issue: [#39451](https://github.com/ant-design/ant-design/issues/39451)
+
 ## How to spell Ant Design correctly?
 
 - ✅ **Ant Design**: Capitalized with space, for the design language.

docs/react/faq.zh-CN.md

@@ -206,6 +206,12 @@ ConfigProvider.config({
 
 因为历史原因，弹层类组件展示命名并不统一，出现了 `open` 与 `visible` 都在使用的情况。这使得非 tsx 用户在开发时遭遇的记忆成本。同样导致新增 feature 时选择何种命名的模棱两可。因而我们希望统一该属性命名，你仍然可以使用原本的 `visible` 它仍然会向下兼容，但是从 v5 起我们将从文档中移除该属性。
 
+## 设置了样式变量 `@line-height-base` 导致布局异常怎么办？
+
+因为 `@line-height-base` 参与了部分组件的布局计算，所以只支持 `number` 类型的单位。如果传入了 `20px`，会被解析成 `20` 进行计算，导致布局异常。
+
+相关 issue：[#39451](https://github.com/ant-design/ant-design/issues/39451)
+
 ## 如何正确的拼写 Ant Design？
 
 - ✅ **Ant Design**：用空格分隔的首字母大写单词，指代设计语言。