*{box-sizing:border-box}body{margin:0;font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Oxygen,Ubuntu,Cantarell,Fira Sans,Droid Sans,Helvetica Neue,sans-serif;-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}#root{width:100%}.app{min-height:100vh;padding:20px;background:linear-gradient(135deg,#667eea,#764ba2)}.app-header{text-align:center;color:#fff;margin-bottom:30px}.app-header h1{font-size:48px;font-weight:800;margin:0;text-shadow:2px 2px 4px rgba(0,0,0,.2)}.subtitle{font-size:18px;margin:10px 0 0;opacity:.9;font-weight:300}.controls{max-width:600px;margin:0 auto 30px;background:#fff;padding:20px;border-radius:12px;box-shadow:0 4px 12px #0000001a}.difficulty-selector{display:flex;gap:10px;margin-bottom:20px;justify-content:center}.difficulty-btn{flex:1;padding:12px 24px;font-size:16px;font-weight:600;border:2px solid #d0d0d0;background:#fff;color:#555;border-radius:8px;cursor:pointer;transition:all .2s ease}.difficulty-btn:hover{border-color:#667eea;color:#667eea;transform:translateY(-2px)}.difficulty-btn.active{background:#667eea;border-color:#667eea;color:#fff}.action-buttons{display:flex;gap:10px;margin-bottom:15px}.action-btn{flex:1;padding:12px 24px;font-size:16px;font-weight:600;border:none;border-radius:8px;cursor:pointer;transition:all .2s ease}.action-btn.new-game{background:#27ae60;color:#fff}.action-btn.new-game:hover{background:#229954;transform:translateY(-2px);box-shadow:0 4px 8px #27ae604d}.action-btn.share{background:#3498db;color:#fff}.action-btn.share:hover{background:#2980b9;transform:translateY(-2px);box-shadow:0 4px 8px #3498db4d}.seed-info{text-align:center;color:#666;font-size:14px;font-weight:500}.game-container{display:flex;justify-content:center;margin-bottom:40px}.instructions{max-width:600px;margin:0 auto;background:#fff;padding:25px;border-radius:12px;box-shadow:0 4px 12px #0000001a}.instructions h3{margin:0 0 15px;color:#2c3e50;font-size:20px}.instructions ul{margin:0;padding-left:20px;color:#555;line-height:1.8}.instructions li{margin-bottom:8px}.instructions strong{color:#2c3e50}@media(max-width:768px){.app{padding:15px}.app-header h1{font-size:36px}.subtitle{font-size:16px}.controls{padding:15px}.difficulty-selector{flex-direction:column}.instructions{padding:20px}}.sudoku-cell{width:100%;height:100%;display:flex;align-items:center;justify-content:center;border:1px solid #d0d0d0;background:#fff;cursor:pointer;font-size:24px;font-weight:600;color:#2c3e50;transition:background-color .15s ease;position:relative}.sudoku-cell:hover{background:#f5f8fa}.sudoku-cell.initial{background:#e8eef2;font-weight:700;color:#1a1a1a;cursor:default}.sudoku-cell.initial:hover{background:#e8eef2}.sudoku-cell.selected{background:#cce5ff;outline:3px solid #4a90e2;outline-offset:-3px;z-index:1}.sudoku-cell.invalid{background:#ffe6e6;color:#d32f2f}.cell-value{-webkit-user-select:none;user-select:none}.cell-notes{display:grid;grid-template-columns:repeat(3,1fr);grid-template-rows:repeat(3,1fr);gap:1px;width:100%;height:100%;padding:2px}.note{display:flex;align-items:center;justify-content:center;font-size:10px;font-weight:500;color:#666;-webkit-user-select:none;user-select:none}.note.active{color:#4a90e2}.sudoku-board-container{display:flex;flex-direction:column;align-items:center;gap:20px}.sudoku-board{display:inline-grid;grid-template-columns:repeat(9,50px);grid-template-rows:repeat(9,50px);border:3px solid #2c3e50;box-shadow:0 4px 12px #00000026;background:#fff}.sudoku-row{display:contents}.sudoku-board>.sudoku-row:nth-child(3n){border-bottom:2px solid #2c3e50}.sudoku-board{gap:0;position:relative}.sudoku-board:before,.sudoku-board:after{content:"";position:absolute;top:0;bottom:0;width:2px;background:#2c3e50;z-index:2;pointer-events:none}.sudoku-board:before{left:150px}.sudoku-board:after{left:300px}.sudoku-board-container:before,.sudoku-board-container:after{content:"";position:absolute;left:3px;right:3px;height:2px;background:#2c3e50;z-index:2;pointer-events:none}.sudoku-board{position:relative}.sudoku-board>:nth-child(3):after,.sudoku-board>:nth-child(6):after{content:"";position:absolute;left:0;right:0;height:2px;background:#2c3e50;z-index:2;pointer-events:none}.sudoku-board{background-image:linear-gradient(to right,#2c3e50 0px,#2c3e50 2px,transparent 2px),linear-gradient(to right,#2c3e50 0px,#2c3e50 2px,transparent 2px),linear-gradient(to bottom,#2c3e50 0px,#2c3e50 2px,transparent 2px),linear-gradient(to bottom,#2c3e50 0px,#2c3e50 2px,transparent 2px);background-size:100% 100%,100% 100%,100% 100%,100% 100%;background-position:150px 0,300px 0,0 150px,0 300px;background-repeat:no-repeat}.completion-message{font-size:24px;font-weight:700;color:#27ae60;text-align:center;padding:20px;background:#e8f8f5;border-radius:8px;border:2px solid #27ae60}@media(max-width:600px){.sudoku-board{grid-template-columns:repeat(9,40px);grid-template-rows:repeat(9,40px);background-position:120px 0,240px 0,0 120px,0 240px}}