In the [bug report] El dialog module, the pop-up window height will not automatically inherit 100%, making the picture displayed outside the pop-up window

### Element UI version
2.13.0

### OS/Browsers version
谷歌 77.0.3865.120

### Vue version
3.0.0-alpha.1

### Reproduction Link
https://github.com/Kevin0109/TopLine

### Steps to reproduce

取 消
确 定

### What is Expected?
图片都显示在弹框中

### What is actually happening?
弹窗高度只有238像素,图片全部显示在弹窗外