* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --primary: #6366f1;
    --primary-dark: #4f46e5;
    --primary-light: #818cf8;
    --success: #10b981;
    --danger: #ef4444;
    --bg-dark: #0f172a;
    --bg-card: #1e293b;
    --bg-card-hover: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #94a3b8;
    --border: #334155;
    --shadow: rgba(0, 0, 0, 0.3);
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
    color: var(--text-primary);
}

.container {
    width: 100%;
    max-width: 600px;
}

.todo-app {
    background: rgba(30, 41, 59, 0.95);
    backdrop-filter: blur(20px);
    border-radius: 24px;
    padding: 32px;
    box-shadow: 0 20px 60px var(--shadow);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.header {
    text-align: center;
    margin-bottom: 32px;
}

.header h1 {
    font-size: 32px;
    font-weight: 700;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 12px;
    margin-bottom: 8px;
}

.header h1 svg {
    stroke: url(#gradient);
    filter: drop-shadow(0 0 8px rgba(102, 126, 234, 0.5));
}

.subtitle {
    color: var(--text-secondary);
    font-size: 14px;
}

.add-todo {
    display: flex;
    gap: 12px;
    margin-bottom: 24px;
}

#todoInput {
    flex: 1;
    padding: 14px 18px;
    background: var(--bg-card);
    border: 2px solid var(--border);
    border-radius: 12px;
    color: var(--text-primary);
    font-size: 15px;
    font-family: inherit;
    transition: all 0.3s ease;
}

#todoInput:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.1);
}

#todoInput::placeholder {
    color: var(--text-secondary);
}

#addBtn {
    padding: 14px 24px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
    border: none;
    border-radius: 12px;
    color: white;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 8px;
    transition: all 0.3s ease;
    font-family: inherit;
}

#addBtn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(99, 102, 241, 0.4);
}

#addBtn:active {
    transform: translateY(0);
}

.stats {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
    margin-bottom: 24px;
}

.stat-item {
    background: var(--bg-card);
    padding: 16px;
    border-radius: 12px;
    text-align: center;
    border: 1px solid var(--border);
    transition: all 0.3s ease;
}

.stat-item:hover {
    background: var(--bg-card-hover);
    transform: translateY(-2px);
}

.stat-label {
    display: block;
    font-size: 12px;
    color: var(--text-secondary);
    margin-bottom: 4px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.stat-value {
    display: block;
    font-size: 24px;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-light) 0%, var(--primary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.todo-list {
    max-height: 400px;
    overflow-y: auto;
    padding-right: 8px;
}

.todo-list::-webkit-scrollbar {
    width: 8px;
}

.todo-list::-webkit-scrollbar-track {
    background: var(--bg-card);
    border-radius: 4px;
}

.todo-list::-webkit-scrollbar-thumb {
    background: var(--primary);
    border-radius: 4px;
}

.todo-list::-webkit-scrollbar-thumb:hover {
    background: var(--primary-dark);
}

.todo-item {
    background: var(--bg-card);
    padding: 16px;
    border-radius: 12px;
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 12px;
    border: 1px solid var(--border);
    transition: all 0.3s ease;
    animation: slideIn 0.3s ease;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.todo-item:hover {
    background: var(--bg-card-hover);
    transform: translateX(4px);
}

.todo-item.completed {
    opacity: 0.6;
}

.todo-checkbox {
    width: 24px;
    height: 24px;
    border: 2px solid var(--border);
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    flex-shrink: 0;
}

.todo-checkbox:hover {
    border-color: var(--primary);
}

.todo-checkbox.checked {
    background: linear-gradient(135deg, var(--success) 0%, #059669 100%);
    border-color: var(--success);
}

.todo-checkbox svg {
    display: none;
    stroke: white;
}

.todo-checkbox.checked svg {
    display: block;
    animation: checkmark 0.3s ease;
}

@keyframes checkmark {
    0% {
        transform: scale(0);
    }
    50% {
        transform: scale(1.2);
    }
    100% {
        transform: scale(1);
    }
}

.todo-text {
    flex: 1;
    font-size: 15px;
    color: var(--text-primary);
    transition: all 0.3s ease;
}

.todo-item.completed .todo-text {
    text-decoration: line-through;
    color: var(--text-secondary);
}

.todo-delete {
    width: 36px;
    height: 36px;
    background: rgba(239, 68, 68, 0.1);
    border: none;
    border-radius: 8px;
    color: var(--danger);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    flex-shrink: 0;
}

.todo-delete:hover {
    background: var(--danger);
    color: white;
    transform: scale(1.1);
}

.empty-state {
    text-align: center;
    padding: 48px 20px;
    color: var(--text-secondary);
}

.empty-state svg {
    margin-bottom: 16px;
    opacity: 0.5;
}

.empty-state p {
    font-size: 16px;
}

@media (max-width: 640px) {
    .todo-app {
        padding: 24px;
    }
    
    .header h1 {
        font-size: 28px;
    }
    
    .add-todo {
        flex-direction: column;
    }
    
    #addBtn {
        justify-content: center;
    }
    
    .stats {
        grid-template-columns: 1fr;
    }
}