mat-expansion-panel - styles get messed up if panel is a child of another element

Bug, feature request, or proposal:

The styles of panels will get messed up in the panels are placed in another element (ex: div)
Please see pseudo-code example below:

<mat-accordion>
  <div>
    <mat-expansion-panel>...</mat-expansion-panel>
  </div>
  <div>
    <mat-expansion-panel>...</mat-expansion-panel>
  </div>
</mat-accordion>

What is the expected behavior?

Panels should be styled correctly

What is the current behavior?

What is the use-case or motivation for changing an existing behavior?

I was trying to implement draggable panels and my implementation has panels inside divs.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Material 7.0.0-beta.2

Is there anything else we should know?

To fix replace lines 15-29 in expansion-panel.scss:

.mat-accordion & {
  &:not(.mat-expanded), &:not(.mat-expansion-panel-spacing) {
    border-radius: 0;
  }

  &:first-of-type {
    border-top-right-radius: $border-radius;
    border-top-left-radius: $border-radius;
  }

  &:last-of-type {
    border-bottom-right-radius: $border-radius;
    border-bottom-left-radius: $border-radius;
  }
}

... with the following:

.mat-accordion & {
  &:not(.mat-expanded), &:not(.mat-expansion-panel-spacing) {
    border-radius: 0;
  }
}

.mat-accordion > &:first-child,
.mat-accordion > &:first-child:not(.mat-expansion-panel) & {
  border-top-right-radius: $border-radius;
  border-top-left-radius: $border-radius;
}

.mat-accordion > &:last-child,
.mat-accordion > *:last-child:not(.mat-expansion-panel) & {
  border-bottom-right-radius: $border-radius;
  border-bottom-left-radius: $border-radius;
}

Bắt đầu trong src/lib/expansion/expansion-panel.scss tại các dòng được tham chiếu 15-29 và tái tạo markup mat-expansion-panel lồng nhau với các wrapper div. So sánh việc thay thế selector được báo cáo với các style hiện có, sau đó xác minh rằng panel đầu tiên và cuối cùng vẫn giữ đúng border radius khi các panel được lồng bên trong các phần tử khác.