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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: #f5f5f5;
    color: #333;
}

.container {
    max-width: 600px;
    margin: 2rem auto;
    padding: 1rem;
}

h1 {
    text-align: center;
    color: #2c3e50;
    margin-bottom: 2rem;
}

.input-container {
    display: flex;
    gap: 0.5rem;
    margin-bottom: 2rem;
}

#todoInput {
    flex: 1;
    padding: 0.8rem;
    border: 2px solid #e0e0e0;
    border-radius: 4px;
    font-size: 1rem;
    transition: border-color 0.3s ease;
}

#todoInput:focus {
    outline: none;
    border-color: #3498db;
}

#addButton {
    padding: 0.8rem 1.5rem;
    background-color: #3498db;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.3s ease;
}

#addButton:hover {
    background-color: #2980b9;
}

#todoList {
    list-style: none;
}

.todo-item {
    display: flex;
    align-items: center;
    padding: 1rem;
    background-color: white;
    border-radius: 4px;
    margin-bottom: 0.5rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    animation: slideIn 0.3s ease;
}

.todo-item.completed {
    background-color: #f8f9fa;
    opacity: 0.7;
}

.todo-item.completed .todo-text {
    text-decoration: line-through;
    color: #6c757d;
}

.todo-checkbox {
    margin-right: 1rem;
    width: 18px;
    height: 18px;
    cursor: pointer;
}

.todo-text {
    flex: 1;
    font-size: 1rem;
}

.delete-btn {
    padding: 0.4rem 0.8rem;
    background-color: #e74c3c;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: background-color 0.3s ease;
}

.delete-btn:hover {
    background-color: #c0392b;
}

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

@media (max-width: 480px) {
    .container {
        margin: 1rem;
        padding: 0.5rem;
    }

    .input-container {
        flex-direction: column;
    }

    #addButton {
        width: 100%;
        margin-top: 0.5rem;
    }
}