What is this PR doing?

• 📰 Update fonts to (largely) use system font stacks.
• 📐 Improves sizing and proportion of chrome to be smaller and better-reflect real-world OS proportions.
• ↔️ Improves responsive collapse of Playground when not in fullscreen/seamless.
• 🔴 Adds reset site functionality (with warning dialog) to red close slot
• ↕️ Add arrow hover-states to buttons
• 👀 Wrap pulsing browser animation in check for prefers reduce motion and fallback to box shadow.

What problem is it solving?

• Helps browser chrome be more-accurate and take up fewer pixels at all screen sizes
• Helps playground collapse better at mobile viewports
• Small improvements for cross-platform/browser render and respecting motion preferences.