* { box-sizing: border-box; font-family: 'Georgia', Tahoma, Geneva, Verdana, sans-serif; }
         body, html { margin: 0; padding: 0; width: 100%; height: 100%; overflow: hidden; background-color: #f7f9fa; /* Clean, pleasant solid background */}
         .classroom-bg { position: relative;max-width: 800px; width: 100%; height: 100%; display: flex; align-items: flex-end; justify-content: space-between; padding: 0 40px; } 
         .top-nav { position: absolute; top: 20px; left: 0; width: 100%; display: flex; justify-content: center; pointer-events: none; z-index: 10; } 
         .btn { background: #ff4757; color: white; border: none; padding: 12px 24px; font-size: 16px; font-weight: bold; border-radius: 25px; cursor: pointer; box-shadow: 0 4px 15px rgba(0,0,0,0.15); transition: all 0.3s ease; pointer-events: auto; text-decoration: none;margin-top:20px; } 
         .btn:hover { transform: translateY(-3px); box-shadow: 0 6px 20px rgba(0,0,0,0.2); background: #ff6b81; } 
         .btn-next { background: #2ed573; position: absolute; bottom: 40px; right: 40px; display: none; /* Hidden until presentation finishes */
         z-index: 10; } 
         .btn-next:hover { background: #2bcbba; } 
         .teacher-container { display: flex; align-items: flex-end; height: 100%; z-index: 2; } 
         .teacher-img { height: 75vh; max-height: 600px; width: auto; display: block; margin-bottom: 0; filter: drop-shadow(4px -2px 8px rgba(0,0,0,0.08)); } 
         .board-container { width: 50%; margin-bottom: 15vh; /* Shifts text nicely into view */
         display: flex; flex-direction: column; justify-content: center; z-index: 3; } 
         .text-line { margin: 15px 0; opacity: 0; transition: opacity 1s ease-in-out; } 
         .tamil-text { font-size: clamp(20px, 2.2vw, 32px); color: #2c3e50; font-weight: bold; display: block; white-space: nowrap; } 
         .sinhala-text { font-size: clamp(16px, 1.6vw, 24px); color: #2ed573; font-weight: bold; display: block; margin-top: 6px; white-space: nowrap; } 
         .visible { opacity: 1; } 
         .start-overlay { position: absolute; top: 0; left: 0; width: 100%; height: 100%; background: rgba(0,0,0,0.65); z-index: 100; display: flex; align-items: center; justify-content: center; backdrop-filter: blur(4px); } 
         @media (max-width: 768px){
         .classroom-bg { padding: 0 10px; } 
         .teacher-container { position: absolute; bottom: 0; left: 0; width: 100%; justify-content: flex-start; pointer-events: none; /* Prevents button touch blocking */}
         .teacher-img { height: 80vh; /* Prominent height on mobile */
         min-height: 380px; max-height: 520px; } 
         .board-container { position: absolute; top: 10%; right: 15px; left: 25px; /* Safely clears teacher's facial space profile */
         width: auto; text-align: right; align-items: flex-end; } 
         .tamil-text { font-size: 1.5rem; text-shadow: 2px 2px 4px rgba(255, 255, 255, 0.9), -2px -2px 4px rgba(255, 255, 255, 0.9); } 
         .sinhala-text { font-size: 1.15rem; color: #16a085; text-shadow: 2px 2px 4px rgba(255, 255, 255, 0.9), -2px -2px 4px rgba(255, 255, 255, 0.9); } 
         .btn-next { bottom: 25px; right: 25px; } 
         }