:root{--background-color: #f4f7f9;--container-bg: #ffffff;--primary-text: #2c3e50;--secondary-text: #7f8c8d;--accent-color: #3498db;--accent-hover: #2980b9;--border-color: #ecf0f1;--danger-color: #e74c3c;--danger-hover: #c0392b;--completed-color: #95a5a6}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;background-color:var(--background-color);color:var(--primary-text)}.app-container{max-width:600px;margin:40px auto;padding:20px;background-color:var(--container-bg);border-radius:8px;box-shadow:0 4px 12px #00000014}.app-header{text-align:center;border-bottom:1px solid var(--border-color);padding-bottom:20px;margin-bottom:20px}.app-header h1{margin:0;font-size:2.5rem;color:var(--primary-text)}.app-header p{margin:5px 0 0;color:var(--secondary-text)}.add-todo-form{display:flex;gap:10px;margin-bottom:20px}.add-todo-form input{flex-grow:1;padding:12px 15px;border:1px solid var(--border-color);border-radius:4px;font-size:1rem}.add-todo-form input:focus{outline:none;border-color:var(--accent-color);box-shadow:0 0 0 2px #3498db33}.add-todo-form button,.todo-item button{padding:12px 20px;border:none;border-radius:4px;background-color:var(--accent-color);color:#fff;font-size:1rem;cursor:pointer;transition:background-color .2s ease}.add-todo-form button:hover{background-color:var(--accent-hover)}.todo-list{list-style-type:none;padding:0;margin:0}.empty-state{text-align:center;color:var(--secondary-text);padding:20px}.todo-item{display:flex;align-items:center;justify-content:space-between;padding:15px;border-bottom:1px solid var(--border-color);transition:background-color .2s ease}.todo-item:last-child{border-bottom:none}.todo-item label{display:flex;align-items:center;cursor:pointer;flex-grow:1}.todo-item input[type=checkbox]{margin-right:15px;width:20px;height:20px;cursor:pointer}.todo-item span{font-size:1.1rem}.todo-item.completed span{text-decoration:line-through;color:var(--completed-color)}.todo-item button{background-color:transparent;border:none;color:var(--danger-color);font-size:1.5rem;cursor:pointer;opacity:0;transition:opacity .2s ease,color .2s ease;padding:0 10px}.todo-item:hover button{opacity:1}.todo-item button:hover{color:var(--danger-hover)}