requirements and problems

as shown in the following figure: https://nghttps://api-v5.segmentfault.com/question/.anthttps://api-v5.segmentfault.com/question/.design/versionhttps://api-v5.segmentfault.com/question/.

1https://api-v5.segmentfault.com/question/. Click the first select, pop-up option (use cdk, to have a layer of backdrop, at this time, if you click somewhere else, it will be blocked by backdrop, so put away the option of the first selecthttps://api-v5.segmentfault.com/question/. )

2https://api-v5.segmentfault.com/question/. If the mouse moves to the second select and clicks, I hope there is a way to click through the backdrop, that is, to turn off the option just opened by the first select, and then pop up the option for the second select;

3https://api-v5.segmentfault.com/question/. If you move the mouse to another place and click, you just need to turn off the option just opened by the first select

the environmental background of the problems and what methods you have tried

ng-zorro 0https://api-v5.segmentfault.com/question/.7https://api-v5.segmentfault.com/question/.x
angular4

refers to the implementation of elementui for vuehttps://api-v5.segmentfault.com/question/. It"s an instruction-based
effecthttps://api-v5.segmentfault.com/question/. See
http://elementhttps://api-v5.segmentfault.com/question/.elemehttps://api-v5.segmentfault.com/question/.io/-sharp/zh-https://api-v5.segmentfault.com/question/.
source code here:
ide.js" rel= "nofollow noreferrer" > https://githubhttps://api-v5.segmentfault.com/question/.com/ElemeFE/elhttps://api-v5.segmentfault.com/question/.
https://githubhttps://api-v5.segmentfault.com/question/.com/ElemeFE/elhttps://api-v5.segmentfault.com/question/.

be implemented in directive in ng?