bug(MatTable): Nested MatTable's rows have no border if I expand last row of parent MatTable
- Dominant language
- TypeScript
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Description
### Is this a regression?
- [ ] Yes, this behavior used to work in the previous version
### The previous version in which this bug was not present was
_No response_
### Description
When I have a nested MatTable set with expand feature, when I expand the last row of the parent table, all the cells in the child MatTable will have no border.

But If I am expanding any other rows except the last row, the nested MatTable is displaying fine.

I have found the reason that the styles from last row .mat-cell of the parent MatTable is being applied to all the child MatTable's .mat-cell

### Reproduction
StackBlitz link: https://stackblitz.com/edit/5djdhn?file=src%2Fexample%2Ftable-expandable-rows-example.ts
Steps to reproduce:
1. Expand the 1st row of the MatTable and check row borders
2. Expand the last row of the MatTable and checkl the absence of row borders of the rows
### Expected Behavior
Only the last row of the nested MatTable will be applied with the `border-bottom: none` styles. not all the rows
### Actual Behavior
Every row inside the last row of MatTable's child MatTable is applied with `border-bottom: none` styles.
### Environment
Angular CLI: 17.0.1
Node: 18.19.0
Package Manager: npm 10.2.3
OS: win32 x64
Angular: 17.0.3
... animations, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router
Package Version
-----------------------------------------------------------
@angular-devkit/architect 0.1700.1
@angular-devkit/build-angular 17.0.1
@angular-devkit/core 17.0.1
@angular-devkit/schematics 17.0.1
@angular/cdk 17.0.1
@angular/cli 17.0.1
@angular/material 17.0.1
@angular/material-luxon-adapter 17.0.1
@schematics/angular 17.0.1
rxjs 7.8.1
typescript 5.2.2
zone.js 0.14.2
Contributor guide
Research direction
Start with the StackBlitz entry point at src/example/table-expandable-rows-example.ts and reproduce the issue by expanding the first row, then the last row. Inspect how the nested MatTable rows receive the parent table's last-row border styling. Done means only the final row of the nested table has border-bottom: none, while the other child rows retain their borders.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- angular, typescript
- Domain
- frontend
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 42/100