With Minerva's dark theme, the share card's light ~~and transparent~~ backgrounds don't seem to display the correct colors:
{F76242980}
Based on T421131#11830668 (thanks @Etonkovidova !).
==Acceptance criteria
[] The share card's light background with Minerva's dark theme has the correct color
[] Share card's transparent background sanity check. Is the current behavior correct?
NOTE: [@background-color-base](https://github.com/wikimedia/mediawiki-extensions-ReaderExperiments/blob/155bbf3d231bf1001879a0ea3882a05ea0309550/resources/experiments/shareHighlight/components/QuoteCard.vue#L261) and [@background-color-transparent](https://github.com/wikimedia/mediawiki-extensions-ReaderExperiments/blob/155bbf3d231bf1001879a0ea3882a05ea0309550/resources/experiments/shareHighlight/components/QuoteCard.vue#L305) are used as background colors. Perhaps they should be updated.