Fix black background on card image areas and imageless cards

[Copilot]

Cards without images render with a black background. Card image areas also lacked an explicit white background, causing issues with transparent images.

Changes in style.css

• .grid-item img: Changed background-color from #f8f9fa → #ffffff
• .grid-item.no-image: Added new rule with background-color: #ffffff to prevent black fill on imageless cards

.grid-item img { width: 100%; height: auto; display: block; background-color: #ffffff; }
.grid-item.no-image { background-color: #ffffff; }

Original prompt

Change card image background to white

Cards without images currently display with a black background. We need to update the CSS to ensure that card image areas (and cards without images) have a white background instead of black.

This involves:

1. Ensuring .grid-item img has a white background
2. Adding a rule for .grid-item.no-image to have a white background so cards without images don't appear black

This pull request was created from Copilot chat.

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.