Fix accordion specificity

[camelburrito]

Fixes #10224

[muxin]

having

amp-accordion > section > :last-child {
  display: none !important;
}
amp-accordion > section[expanded] > :last-child {
  display: block !important;
}

instead of

amp-accordion > section > .i-amphtml-accordion-content {		
  display: none !important;		
}		
amp-accordion > section[expanded] > .i-amphtml-accordion-content {		
  display: block !important;		
}

is ok?

[camelburrito]

@muxin - yes that is ok since they have the same specificity

[cramforce]

Thanks for the quick fix. Is there a way to revert this? The previous state was better (modulo bad specificity) because it didn't FOUCed when the extension loaded late.