🎨 Palette: Semantic Keyboard Shortcuts

[EiJackGH]

💡 What: Added semantic <kbd> tags around the keyboard shortcuts ("Space" and "↑") in the instruction overlay and provided physical key styling (borders, drop shadows, and high-contrast text) via the internal <style> block.

🎯 Why: Improves the micro-UX of the game by making the interactive controls immediately obvious and discoverable. Highlighting keyboard shortcuts to look like physical keys makes the interface far more intuitive for new users jumping into the game.

📸 Before/After:
Before: Plain text instruction "Press Space or ↑ to jump!" hovering on the screen.
After: The words "Space" and "↑" look like physical keyboard buttons (gray background, shadow, monospace font), standing out clearly from the rest of the text.

♿ Accessibility: Increased semantic meaning by utilizing native <kbd> tags. It signals to screen readers and browsers that these are explicitly keyboard inputs.

Rationale for Custom CSS: The mario-game.njk file does not utilize a utility CSS framework like Tailwind, and styling is strictly managed via a plain internal <style> block. Adding the kbd CSS rule directly into this block matches the existing architectural pattern of the file.

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PR created automatically by Jules for task 8714611961810808631 started by @EiJackGH

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