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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    background: white;
    border-radius: 15px;
    box-shadow: 0 10px 40px rgba(0, 0, 0, 0.2);
    padding: 40px;
    width: 100%;
    max-width: 600px;
}

h1 {
    text-align: center;
    color: #333;
    margin-bottom: 30px;
    font-size: 2em;
}

.input-section {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
}

#todoInput {
    flex: 1;
    padding: 12px 15px;
    border: 2px solid #e0e0e0;
    border-radius: 8px;
    font-size: 16px;
    transition: border-color 0.3s;
}

#todoInput:focus {
    outline: none;
    border-color: #667eea;
}

#addBtn {
    padding: 12px 30px;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 16px;
    font-weight: bold;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
}

#addBtn:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(102, 126, 234, 0.4);
}

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

.filter-section {
    display: flex;
    gap: 10px;
    margin-bottom: 20px;
    justify-content: center;
}

.filter-btn {
    padding: 8px 20px;
    background: #f5f5f5;
    border: 2px solid #e0e0e0;
    border-radius: 20px;
    cursor: pointer;
    transition: all 0.3s;
    font-size: 14px;
}

.filter-btn:hover {
    background: #e0e0e0;
}

.filter-btn.active {
    background: #667eea;
    color: white;
    border-color: #667eea;
}

#todoList {
    list-style: none;
    margin-bottom: 20px;
}

.todo-item {
    display: flex;
    align-items: center;
    gap: 15px;
    padding: 15px;
    background: #f9f9f9;
    border-radius: 8px;
    margin-bottom: 10px;
    transition: all 0.3s;
}

.todo-item:hover {
    background: #f0f0f0;
    transform: translateX(5px);
}

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

.todo-item input[type="checkbox"] {
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.todo-item span {
    flex: 1;
    font-size: 16px;
    color: #333;
}

.todo-item.completed span {
    text-decoration: line-through;
    color: #999;
}

.delete-btn {
    padding: 6px 12px;
    background: #ff4757;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 14px;
    transition: background 0.3s;
}

.delete-btn:hover {
    background: #ff3838;
}

.stats {
    text-align: center;
    color: #666;
    font-size: 14px;
    padding-top: 10px;
    border-top: 2px solid #e0e0e0;
}

/* ローディングとエラーメッセージ */
.loading-message,
.empty-message,
.error-message {
    text-align: center;
    padding: 30px;
    color: #999;
    font-size: 16px;
}

.error-message {
    color: #ff4757;
}

#addBtn:disabled,
#todoInput:disabled,
.todo-item input[type="checkbox"]:disabled,
.delete-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* レスポンシブデザイン */
@media (max-width: 600px) {
    .container {
        padding: 20px;
    }

    h1 {
        font-size: 1.5em;
    }

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

    #addBtn {
        width: 100%;
    }

    .filter-section {
        flex-wrap: wrap;
    }
}