fix: demo css conflict

src/packages/checkbox/demo.vue

@@ -194,12 +194,6 @@ export default createDemo({
   }
 });
 </script>
-<style>
-#app {
-  height: auto;
-  background: #f6f7f9;
-}
-</style>
 <style lang="scss" scoped>
 .demo-list {
   margin: 57px 0 60px 0;

src/packages/collapse/demo.vue

@@ -107,12 +107,6 @@ export default createDemo({
 });
 </script>
 
-<style>
-#app {
-  height: auto;
-  background: #f7f8fa;
-}
-</style>
 <style lang="scss" scoped>
 .demo-list {
   padding-top: 0;

src/packages/radio/demo.vue

@@ -124,12 +124,6 @@ export default createDemo({
 });
 </script>
 
-<style>
-#app {
-  height: auto;
-  background: #f6f7f9;
-}
-</style>
 <style lang="scss" scoped>
 .demo-list {
   margin: 57px 0 60px 0;