- CSS: .code-block-wrapper with relative positioning
- CSS: .copy-code-btn with hover opacity transition (hidden until hover)
- CSS: .copied state (green accent) after successful copy
- viewer.js: wraps each <pre> in .code-block-wrapper + appends copy button
- popout.html: same logic with vanilla JS (ES5 compatible)
- Button: 'Copier' → '✓ Copié' on click, reverts after 2s
- Toast: showToast('Code copié dans le presse-papiers') via navigator.clipboard