Backtop 
A button to back to top.
Basic Usage 
Scroll down to see the bottom-right button.
Customizations 
Display area is 40px * 40px.
API 
Attributes 
| Name | Description | Type | Default | 
|---|---|---|---|
| target | the target to trigger scroll. | string | — | 
| visibility-height | the button will not show until the scroll height reaches this value. | number | 200 | 
| right | right distance. | number | 40 | 
| bottom | bottom distance. | number | 40 | 
Events 
| Name | Description | Parameters | 
|---|---|---|
| click | triggers when click. | Function | 
Slots 
| Name | Description | 
|---|---|
| default | customize default content. |