docs(collapse): default expand demo

src/collapse/demos/enUS/default-expanded.demo.md

@@ -1,6 +1,8 @@
 # Default Expanded
 
-You can set which panels are expanded by default. For example, we can set `red light` and `amber light` to be expanded by default, and set `flashing` to be expanded when `green light` is expanded. It should be noted that even if only one panel you want to set to be expanded, `default-expanded-names` should also be passed in an array, unless `accordion` is set to `true`.
+You can set which panels are expanded by default. For example, we can set 'red light' and 'amber light' to be expanded by default.
+
+It should be noted that even if only one panel you want to set to be expanded, `default-expanded-names` should also be passed in an array, unless `accordion` is set to `true`.
 
 ```html
 <n-collapse :default-expanded-names="['2', '3']">

src/collapse/demos/zhCN/default-expanded.demo.md

@@ -1,6 +1,8 @@
 # 默认展开
 
-可以设置哪些面板默认展开。如我们可以设置`红灯`和`黄灯`默认展开，当`绿灯`展开时`闪烁`展开。应当注意的是，即使只打算展开一个面板，`default-expanded-names`也应当传入数组，除非使用了`accordion`。
+可以设置哪些面板默认展开。如我们可以设置“红灯”和“黄灯”默认展开。
+
+应当注意的是，即使只打算展开一个面板，`default-expanded-names`也应当传入数组，除非使用了`accordion`。
 
 ```html
 <n-collapse :default-expanded-names="['2', '3']">