.history-section {
    background-color: #f8f9fa;
    padding: 100px 0;
}

.timeline {
    position: relative;
    max-width: 800px;
    position: relative;
    max-width: 800px;
    margin: 0 auto;
    padding: 0 20px;
    list-style: none;
}

/* 縦線 */
.timeline::before {
    content: '';
    position: absolute;
    top: 0;
    bottom: 0;
    left: 22px; /* 調整: 22pxに変更 */
    width: 4px;
    background: #e0e0e0;
    z-index: 1;
}

/* タイムラインアイテム */
.timeline-item {
    position: relative;
    margin-bottom: 50px;
    padding-left: 60px;
}

/* 最後のアイテムの下マージンを消す */
.timeline-item:last-child {
    margin-bottom: 0;
}

/* 丸いノード */
.timeline-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: 10px; /* 調整: 10pxに変更（縦線の中央に正確に配置） */
    width: 28px;
    height: 28px;
    border-radius: 50%;
    background: var(--primary-color);
    border: 4px solid #fff;
    z-index: 2;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

/* タイムラインコンテンツ */
.timeline-content {
    position: relative;
    padding: 20px;
    background: #fff;
    border-radius: 8px;
    box-shadow: 0 3px 10px rgba(0,0,0,0.1);
    transition: all 0.3s ease;
}

.timeline-content:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
}

/* コンテンツボックスの矢印 */
.timeline-content::before {
    content: '';
    position: absolute;
    top: 15px;
    left: -10px;
    width: 0;
    height: 0;
    border-top: 10px solid transparent;
    border-bottom: 10px solid transparent;
    border-right: 10px solid #fff;
    z-index: 3;
}

/* 日付（年）スタイル */
.timeline-year {
    display: inline-block;
    background: linear-gradient(135deg, var(--primary-color), #2980b9);
    color: white;
    padding: 8px 16px;
    border-radius: 20px;
    font-weight: bold;
    font-size: 0.9rem;
    margin-bottom: 15px;
    box-shadow: 0 3px 10px rgba(52, 152, 219, 0.3);
}

/* コンテンツ内の見出し */
.timeline-content h3 {
    margin-top: 0;
    margin-bottom: 10px;
    color: var(--primary-color);
    font-size: 1.4rem;
    font-weight: 600;
}

/* コンテンツ内の段落 */
.timeline-content p {
    color: #666;
    line-height: 1.6;
    font-size: 1rem;
    margin-bottom: 15px;
}

/* コンテンツ内の最後の要素のマージンを消す */
.timeline-content *:last-child {
    margin-bottom: 0;
}

/* コンテンツ内の画像 */
.timeline-content img {
    max-width: 100%;
    border-radius: 4px;
    margin: 10px 0;
}

/* スキル進歩セクション */
.skill-progress-section {
    padding: 100px 0;
    background: white;
}

.skill-timeline {
    max-width: 800px;
    margin: 0 auto;
}

.skill-item {
    display: flex;
    align-items: flex-start;
    gap: 30px;
    margin-bottom: 50px;
    padding: 30px;
    background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
    border-radius: 15px;
    border-left: 5px solid var(--primary-color);
    transition: all 0.3s ease;
}

.skill-item:hover {
    transform: translateX(10px);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
}

.skill-year {
    flex-shrink: 0;
    width: 80px;
    height: 80px;
    background: linear-gradient(135deg, var(--primary-color), #2980b9);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    font-size: 1.1rem;
    box-shadow: 0 5px 15px rgba(52, 152, 219, 0.3);
}

.skill-content h3 {
    color: var(--secondary-color);
    margin-bottom: 10px;
    font-size: 1.3rem;
}

.skill-content p {
    color: #666;
    margin-bottom: 15px;
    line-height: 1.6;
}

.skill-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
}

.tag {
    background: var(--primary-color);
    color: white;
    padding: 5px 12px;
    border-radius: 15px;
    font-size: 0.8rem;
    font-weight: 500;
}

/* レスポンシブデザイン */
@media (max-width: 768px) {
    .timeline::before {
        left: 17px; /* モバイル用調整 */
    }

    .timeline-item {
        padding-left: 50px;
    }

    .timeline-item::before {
        left: 5px; /* モバイル用調整 */
        width: 24px;
        height: 24px;
    }

    .timeline-content {
        padding: 15px;
    }

    .timeline-content::before {
        left: -8px;
        border-top: 8px solid transparent;
        border-bottom: 8px solid transparent;
        border-right: 8px solid #fff;
    }

    .timeline-year {
        font-size: 0.8rem;
        padding: 6px 12px;
    }

    .timeline-content h3 {
        font-size: 1.2rem;
    }

    .skill-item {
        flex-direction: column;
        text-align: center;
        gap: 20px;
        padding: 20px;
    }

    .skill-year {
        width: 60px;
        height: 60px;
        font-size: 1rem;
        margin: 0 auto;
    }

    .skill-tags {
        justify-content: center;
    }
}

/* アニメーション */
@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.timeline-item {
    animation: fadeInUp 0.6s ease-out;
}

.skill-item {
    animation: fadeInUp 0.6s ease-out;
}

a {
  text-decoration: none;
}