[6.0] Make Card's link position to be relative instead of absolute

[mportiz08]

• Explanation: Updates card abstract/title/link positioning and layout
• Scope: Impacts pages using cards, especially in smaller viewport widths
• Issue: rdar://128642639
• Risk: Low, focused CSS-only changes to specific component
• Testing: Manually checked that smaller viewport positioning is improved and no regressions with styling of cards across varying viewport sizes
• Reviewer: @mportiz08
• Original PR: #837

\cc @marinaaisa

[mportiz08]

@swift-ci test