:root {
    --primary-color: #0891b2; /* cyan-600 */
    --primary-color-dark: #0e7490; /* cyan-700 */
    --primary-color-light: #ecfeff; /* cyan-50 */
    --text-color-dark: #1e293b; /* slate-800 */
    --text-color: #334155; /* slate-700 */
    --text-color-light: #64748b; /* slate-500 */
    --bg-color: #f0f9ff; /* sky-50 */
    --card-bg-color: #ffffff;
    --border-color: #e2e8f0; /* slate-200 */
    --success-color: #10b981; /* emerald-500 */
    --error-color: #ef4444; /* red-500 */
    --shadow-color: rgba(8, 145, 178, 0.1);
    
    /* Venn Diagram (kulaka l04) Styles */
    --set-a-color: rgba(56, 189, 248, 0.6); 
    --set-b-color: rgba(251, 146, 60, 0.6);
    --set-a-border: #0284c7;
    --set-b-border: #f97316;
    --universal-border: #94a3b8;
}

@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes slideInUp { from { transform: translateY(40px); opacity: 0; } to { transform: translateY(0); opacity: 1; } }
@keyframes starPop { 0% { transform: scale(1); } 50% { transform: scale(1.3); } 100% { transform: scale(1); } }
@keyframes levelUpPop { 0% { transform: scale(0) rotate(-180deg); opacity: 0; } 50% { transform: scale(1.2) rotate(10deg); } 100% { transform: scale(1) rotate(0deg); opacity: 1; } }
@keyframes starPulse { 0%, 100% { transform: scale(1); } 50% { transform: scale(1.3); } }
@keyframes pulse-effect { 0%, 100% { transform: scale(1); } 50% { transform: scale(1.15); } }

body { margin: 0; padding: 0; font-family: 'Noto Sans Sinhala', 'Poppins', sans-serif; background-color: var(--bg-color); color: var(--text-color); line-height: 1.8; visibility: hidden; }
body.loaded { visibility: visible; }
.page-container { max-width: 900px; margin: 0 auto; width: 100%; min-height: 100vh; padding: 24px 16px; box-sizing: border-box; }
.lesson-header { display: flex; justify-content: space-between; align-items: center; padding-bottom: 16px; margin-bottom: 24px; animation: fadeIn 0.5s ease-out; }
.lesson-title h1 { font-size: 26px; font-weight: 800; color: var(--primary-color-dark); margin: 0; line-height: 1.2; }
.lesson-title span { font-size: 14px; font-weight: 500; color: var(--text-color-light); }
.back-link { display: flex; align-items: center; text-decoration: none; font-size: 14px; font-weight: 600; color: var(--primary-color-dark); padding: 8px 12px; border-radius: 8px; transition: all 0.3s; border: 1px solid var(--border-color); background-color: var(--card-bg-color); }
.back-link:hover { background-color: var(--primary-color-light); transform: scale(1.05); }
.back-link svg { width: 20px; height: 20px; margin-right: 8px; transition: transform 0.3s; }
.back-link:hover svg { transform: translateX(-3px); }
.progress-section { background-color: var(--card-bg-color); border-radius: 16px; padding: 20px; margin-bottom: 40px; border: 1px solid var(--border-color); box-shadow: 0 4px 15px var(--shadow-color); animation: slideInUp 0.6s ease-out; }
.progress-label { font-size: 14px; font-weight: 600; color: var(--text-color-dark); margin-bottom: 12px; display: flex; justify-content: space-between; }
#progress-text { color: var(--primary-color); }
.progress-bar-container { width: 100%; height: 12px; background-color: #e2e8f0; border-radius: 6px; overflow: hidden; }
.progress-bar { width: 0%; height: 100%; background: linear-gradient(90deg, #67e8f9, var(--primary-color)); border-radius: 6px; transition: width 0.8s cubic-bezier(0.25, 1, 0.5, 1); }
.concepts-grid { display: grid; grid-template-columns: 1fr; gap: 32px; }
.animated-card { opacity: 0; transition: opacity 0.6s ease-out, transform 0.6s ease-out; transform: translateY(30px); }
.animated-card.in-view { opacity: 1; transform: translateY(0); }
.concept-card { background-color: var(--card-bg-color); border: 1px solid var(--border-color); border-radius: 16px; box-shadow: 0 4px 15px var(--shadow-color); transition: transform 0.3s, box-shadow 0.3s; overflow: hidden; }
.concept-card:hover { transform: translateY(-8px); box-shadow: 0 12px 25px var(--shadow-color); }
.card-header { padding: 20px 24px; border-bottom: 1px solid var(--border-color); background-color: var(--primary-color-light); }
.card-header h2 { font-size: 20px; font-weight: 700; margin: 0; color: var(--primary-color-dark); display: flex; align-items: center; justify-content: space-between; }
.card-header h2 .card-icon { margin-right: 12px; }
.completion-star { font-size: 24px; color: #d1d5db; transition: color 0.3s, transform 0.3s; }
.concept-card.star-earned .completion-star { color: #facc15; transform: scale(1.1); animation: starPop 0.4s ease-out; }
.card-body { padding: 24px; }
.card-body p { margin: 0 0 16px 0; font-size: 15px; }
.example-text { font-style: italic; color: var(--text-color-light); border-left: 3px solid var(--primary-color); padding-left: 10px; }
.interactive-example { margin-top: 24px; padding-top: 20px; border-top: 1px dashed var(--border-color); }
.interactive-example:first-child { margin-top: 0; padding-top: 0; border-top: none; }
.interactive-example .question { font-weight: 600; color: var(--text-color-dark); margin-bottom: 12px; font-size: 15px; }
.options-container { display: flex; flex-wrap: wrap; gap: 10px; }
.option-btn { padding: 8px 16px; border-radius: 8px; border: 2px solid var(--border-color); background-color: var(--card-bg-color); color: var(--text-color); font-weight: 600; cursor: pointer; transition: all 0.2s ease-in-out; }
.option-btn:hover:not(:disabled) { border-color: var(--primary-color); background-color: var(--primary-color-light); transform: translateY(-2px); }
.option-btn.correct { background-color: #dcfce7; border-color: #10b981; color: #10b981; }
.option-btn.incorrect { background-color: #fee2e2; border-color: #ef4444; color: #ef4444; }
.option-btn:disabled { cursor: not-allowed; opacity: 0.7; }
.feedback-message { margin-top: 12px; font-size: 14px; font-weight: 500; min-height: 20px; padding: 5px; border-radius: 5px; }
.feedback-message.correct { color: #059669; background-color: #ecfdf5;}
.feedback-message.incorrect { color: #dc2626; background-color: #fef2f2;}
.concept-card.star-earned { border-left: 4px solid var(--success-color); }
.summary-card ul { list-style: none; padding: 0; }
.summary-card li { display: flex; align-items: flex-start; gap: 12px; margin-bottom: 12px; }
.summary-card .summary-icon { flex-shrink: 0; width: 20px; height: 20px; color: var(--success-color); margin-top: 4px; }
.next-lesson-btn { display: none; width: fit-content; margin: 20px auto 0 auto; background-color: var(--primary-color); color: white; padding: 12px 24px; border-radius: 8px; text-decoration: none; font-weight: 600; transition: all 0.3s; }
.next-lesson-btn:hover { background-color: var(--primary-color-dark); transform: translateY(-2px); box-shadow: 0 4px 10px rgba(0,0,0,0.1); }
.page-container.session-complete .next-lesson-btn { display: block; }
#confetti-canvas { position: fixed; top: 0; left: 0; width: 100%; height: 100%; z-index: 9999; pointer-events: none; display: none; }
#level-up-modal { position: fixed; inset: 0; z-index: 10000; display: flex; align-items: center; justify-content: center; background-color: rgba(0,0,0,0.6); opacity: 0; visibility: hidden; transition: opacity 0.3s, visibility 0.3s; }
#level-up-modal.visible { opacity: 1; visibility: visible; }
.level-up-content { background-color: white; border-radius: 24px; box-shadow: 0 10px 30px rgba(0,0,0,0.2); max-width: 380px; width: 90%; text-align: center; animation: levelUpPop 0.6s ease-out forwards; padding: 24px;}
.level-up-card { border-radius: 16px; padding: 24px; color: white; }
.level-up-card .emoji { font-size: 56px; margin-bottom: 16px; }
.level-up-card h3 { font-size: 28px; font-weight: 800; margin: 0 0 8px 0; }
.level-up-stars { display: flex; justify-content: center; gap: 4px; margin-bottom: 16px; }
.level-up-stars svg { width: 32px; height: 32px; color: rgba(255, 255, 255, 0.3); }
.level-up-stars svg.filled { color: #fde047; animation: starPulse 0.5s ease-in-out; }
.level-up-card .level-name { font-size: 32px; font-weight: 800; margin-bottom: 8px; }
.level-up-card .level-message { font-size: 16px; opacity: 0.9; }
.gradient-genius { background-image: linear-gradient(to right, #fca5a5, #ef4444); }
.gradient-expert { background-image: linear-gradient(to right, #c084fc, #f472b6); }
.gradient-scholar { background-image: linear-gradient(to right, #60a5fa, #38bdf8); }
.gradient-learner { background-image: linear-gradient(to right, #4ade80, #22c55e); }
.gradient-beginner { background-image: linear-gradient(to right, #9ca3af, #6b7280); }
#achievements-section h3 { font-weight: 700; color: var(--text-color-dark); font-size: 18px; text-align: center; margin-bottom: 16px; }
.achievement-badges { display: flex; gap: 15px; flex-wrap: wrap; justify-content: center; margin-top: 15px; }
.badge { width: 60px; height: 60px; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 24px; position: relative; cursor: pointer; transition: all 0.3s ease; }
.badge::after { content: attr(data-tooltip); position: absolute; bottom: -35px; left: 50%; transform: translateX(-50%); background: var(--text-color-dark); color: white; padding: 5px 10px; border-radius: 5px; font-size: 12px; font-family: 'Poppins', 'Noto Sans Sinhala', sans-serif; white-space: nowrap; opacity: 0; pointer-events: none; transition: opacity 0.3s; z-index: 10; }
.badge:hover::after { opacity: 1; }
.badge.earned { background: linear-gradient(135deg, #fbbf24, #f59e0b); box-shadow: 0 4px 10px rgba(245, 158, 11, 0.3); transform: scale(1.1); color: white; }
.badge.locked { background: #e5e5e5; color: #a1a1aa; opacity: 0.7; }

/* Venn Diagram (kulaka l04) */
.venn-diagram-container-wrapper { display: flex; flex-direction: column; gap: 1.5rem; }
@media (min-width: 768px) { .venn-diagram-container-wrapper { flex-direction: row; align-items: flex-start; } }
.venn-diagram-card { flex-grow: 1; display: flex; flex-direction: column; align-items: center; }
.controls-card { flex-shrink: 0; width: 100%; }
@media (min-width: 768px) { .controls-card { width: 280px; } }
.controls-card h3 { margin-top: 0; color: var(--text-color-dark); border-bottom: 2px solid var(--border-color); padding-bottom: 0.75rem; margin-bottom: 1rem; }
.control-buttons { display: grid; grid-template-columns: 1fr 1fr; gap: 0.75rem; }
.control-buttons button { background-color: transparent; border: 1px solid var(--border-color); border-radius: 0.5rem; padding: 0.75rem; cursor: pointer; font-family: inherit; font-size: 0.95rem; font-weight: 700; transition: background-color 0.2s, color 0.2s, transform 0.2s; text-align: center; }
.control-buttons button:hover { background-color: var(--primary-color-light); transform: translateY(-2px); }
.control-buttons button.active { color: white; }
#btn-a.active { background-color: var(--set-a-border); }
#btn-b.active { background-color: var(--set-b-border); }
#btn-intersection.active, #btn-union.active { background-color: #6d28d9; }
#btn-reset.active { background-color: var(--text-color); }
.venn-diagram-container { width: 100%; max-width: 400px; aspect-ratio: 4 / 3; position: relative; }
.universal-set { width: 100%; height: 100%; border: 3px solid var(--universal-border); border-radius: 1rem; position: relative; background-color: #f8fafc; }
.universal-set-label { position: absolute; top: 0.5rem; left: 1rem; font-size: 1.5rem; font-weight: 700; color: var(--universal-border); }
.circle { width: 65%; height: 85%; border-radius: 50%; position: absolute; top: 50%; transform: translateY(-50%); transition: all 0.3s ease-in-out; }
.circle-a { left: 5%; background-color: var(--set-a-color); border: 3px solid var(--set-a-border); }
.circle-b { right: 5%; background-color: var(--set-b-color); border: 3px solid var(--set-b-border); }
.circle.highlight { transform: translateY(-50%) scale(1.05); box-shadow: 0 0 20px 5px currentColor; }
.circle-a.highlight { color: var(--set-a-color); }
.circle-b.highlight { color: var(--set-b-color); }
.circle.dimmed { opacity: 0.2; }
.set-label { position: absolute; font-size: 1.5rem; font-weight: 700; top: 5%; }
.label-a { left: 18%; color: var(--set-a-border); }
.label-b { right: 18%; color: var(--set-b-border); }
.element { position: absolute; font-size: 1.1rem; font-weight: 700; }
.static-venn { max-width: 250px; margin: 1rem auto; display: block; }

/* Animation (samikarana) Styles */
.animation-wrapper { background-color: var(--primary-color-light); border-radius: 12px; padding: 20px; margin-top: 20px; }
.animation-container { background-color: rgba(255, 255, 255, 0.5); border-radius: 12px; padding: 1rem; display: flex; flex-direction: column; align-items: center; justify-content: center; font-family: 'Poppins', sans-serif; font-weight: 700; color: var(--primary-color-dark); min-height: 250px; position: relative; }
.step-box { transition: all 0.5s cubic-bezier(0.25, 0.8, 0.25, 1); opacity: 0; transform: translateY(20px); position: absolute; display: flex; align-items: center; justify-content: center; flex-wrap: wrap; font-size: clamp(1.5rem, 5vw, 2.2rem); text-align: center; }
.step-box.visible { opacity: 1; transform: translateY(0); }
.anim-btn { padding: 8px 16px; border-radius: 8px; border: none; background-color: var(--primary-color); color: white; font-weight: 600; cursor: pointer; transition: all 0.2s; }
.anim-btn:hover { background-color: var(--primary-color-dark); transform: translateY(-2px); }
.explanation { text-align: center; color: var(--primary-color-dark); font-weight: 600; min-height: 2.5em; }
.pulse { animation: pulse-effect 1s ease-in-out; }