/* --- Section 3: Flow (STAGGERED ENTRANCE) --- */
#section_3 {
    position: relative;
    height: 800vh; /* 滞在時間を伸ばすためにスクロール領域をさらに延長 */
    background: var(--bg);
    color: var(--text);
}

.sec3-sticky-wrapper {
    position: sticky;
    top: 0;
    width: 100%;
    height: 100vh;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    background: #fcfcfc; /* セクションの境界を分かりやすくする極薄いグレー */
}

.sec3-card {
    width: 90%;
    max-width: 450px;
    background: #fff;
    padding: clamp(30px, 5vw, 60px);
    border: 1px solid #eee;
    border-top: 5px solid var(--primary);
    position: absolute;
    box-shadow: 0 40px 100px rgba(0,0,0,0.05);
    opacity: 0;
    pointer-events: none;
    border-radius: 8px;
    will-change: transform, opacity;
}

.sec3-step-num {
    color: var(--primary);
    font-weight: 900;
    margin-bottom: 10px;
    font-family: var(--font-display);
    letter-spacing: 0.1em;
}

.sec3-title {
    font-family: var(--font-serif);
    font-size: clamp(1.5rem, 3vw, 2rem);
    font-weight: 900;
    margin-bottom: 20px;
}

.sec3-desc {
    color: #666;
    line-height: 1.8;
}

.sec3-img {
    width: 100%;
    margin-top: 30px;
    border-radius: 4px;
}

.sec3-separator {
    position: absolute;
    width: 90%;
    max-width: 400px;
    text-align: center;
    font-family: var(--font-serif);
    font-style: italic;
    color: var(--primary);
    font-size: clamp(1.2rem, 3vw, 1.5rem);
    opacity: 0;
    pointer-events: none;
    line-height: 1.8;
    will-change: transform, opacity;
}

/* Video Area */
.sec3-video-area {
    position: absolute;
    width: 100%;
    height: 100vh;
    background: #000;
    color: #fff;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    opacity: 0;
    visibility: hidden;
    z-index: 100;
    transition: opacity 0.5s ease, visibility 0.5s ease;
}

.sec3-video-title {
    font-family: var(--font-serif);
    font-size: clamp(1.5rem, 4vw, 3rem);
    font-weight: 900;
    margin-bottom: clamp(20px, 4vw, 40px);
    text-align: center;
}

.sec3-video-box {
    width: 90%;
    max-width: 900px;
    aspect-ratio: 16/9;
    background: #222;
    position: relative;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 20px 60px rgba(0,122,255,0.2);
}

.sec3-video-box iframe {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
}