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

html,
body{

    width:100%;
    min-height:100%;

    overflow-x:hidden;

    background:#ffffff;

    font-family:"Be Vietnam Pro",sans-serif;
    color:#000000;

}

html{

    overflow-y:scroll;
    scrollbar-gutter:stable;

}

h1{

    font-family:'Lost Vietnam', serif;

    font-size:clamp(3rem, 8vw, 8rem);

}

a{

    color:#c75739;

}


/* =========================
   NAVBAR
========================= */

#navbar{

    position:absolute;

    top:5px;
    left:0;

    width:100%;

    display:flex;

    justify-content:space-around;
    align-items:center;

    z-index:1000;

    transition:background-color .3s ease, padding .3s ease;

}

#navbar a{

    font-family:'Lost Vietnam';

    font-size:2rem;

    color:#C75739;

    text-decoration:none;

}

#navbar a:hover{

    text-decoration:underline;

}

#nav-middle{

    display:flex;

    justify-content:center;
    align-items:center;

}

#nav-logo{

    width:100px;

    height:auto;

    display:block;

}

#nav-home{

    display:none;

}

#navbar.scrolled{

    position:fixed;

    top:0;

    background:#C75739;

    padding:7px 0;

}

#navbar.scrolled a{

    color:white;

}

#navbar.scrolled #nav-logo{

    display:none;

}

#navbar.scrolled #nav-home{

    display:block;

}


/* =========================
   SECTION 1: HERO
========================= */

.hero{

    position:relative;

    height:100vh;

}

.hero img{

    width:100%;
    height:100%;

    object-fit:cover;

}

.hero-overlay{

    position:absolute;

    inset:0;

    display:flex;

    flex-direction:column;

    justify-content:center;
    align-items:center;

    color:white;

    text-align:center;

    text-shadow:2px 2px 4px #000000;

}

.hero-overlay p{

    font-size:clamp(1rem, 2.5vw, 1.5rem);

}


/* =========================
   SECTION 2: STORY (bút ký)
========================= */

.story{
    position:relative;
    max-width:1180px;
    margin:0 auto;
    padding:120px 24px 160px;
}

:root{

    --rhythm:56px;    /* khoảng cách dọc mặc định giữa 2 node */
    --overlap:110px;  /* kéo node bên phải (chẵn) lên, tạo cảm giác chạy song song/so le */
    --cluster-gap:-30px; /* khoảng cách riêng giữa các ảnh trong bộ 4-9 (liên quan nhau) */

    --font-scale:1;   /* nút đổi cỡ chữ CHỈ tác động lên text trong section 2 */

}

body.font-big{ --font-scale:1.25; }
body.font-small{ --font-scale:.8; }

.story-track{
    position:relative;
    display:flex;
    flex-direction:column;
    z-index:2;
}

/* sợi chỉ nối - vẽ bằng JS, nằm dưới các node */
.story-thread{
    position:absolute;
    inset:0;
    width:100%;
    height:100%;
    z-index:1;
    overflow:visible;
    pointer-events:none;
}

.story-thread path{
    fill:none;
    stroke:#C75739;
    stroke-width:1.6;
    stroke-linecap:round;
    stroke-linejoin:round;
    opacity:.55;
}

/* ---------- NODE CHUNG ---------- */

.story-node{
    position:relative;
    max-width:46%;
    opacity:0;
    transition:opacity .8s ease;
    margin-top:var(--rhythm);
}

.story-node.is-visible{
    opacity:1;
}

.story-node:first-child{
    margin-top:0;
}

.story-node:nth-child(odd){
    align-self:flex-start;
}

.story-node:nth-child(even){
    align-self:flex-end;
    margin-top:calc(var(--rhythm) - var(--overlap));
}

/* chỉ áp dụng khoảng cách hẹp GIỮA 2 ảnh liên tiếp cùng thuộc bộ 4-9,
   không đụng tới khoảng cách trước/sau khi vào/ra khỏi bộ ảnh này */
.story-node.is-cluster + .story-node.is-cluster{
    margin-top:var(--cluster-gap);
}

/* ---------- NODE: ẢNH ---------- */

.story-image{
    display:inline-block;
    border:1px solid #e7ddd2;
    border-radius:4px;
    padding:10px;
    background:#fffdfb;
    box-shadow:0 12px 30px rgba(43,38,34,.06);
}

.story-image img{
    display:block;
    max-width:100%;
    height:auto;
    border-radius:2px;
}

.story-image.is-portrait{
    width:min(300px, 30vw);
}

.story-image.is-landscape{
    width:min(460px, 44vw);
}

/* ---------- NODE: TEXT ---------- */

.story-text{
    border:1px solid #e7ddd2;
    border-radius:4px;
    padding:32px 36px;
    background:#fffdfb;
    box-shadow:0 12px 30px rgba(43,38,34,.06);
    font-size:calc(1.15rem * var(--font-scale));
    line-height:1.75;
    color:#3a332d;
}

.story-text p + p{
    margin-top:1em;
}

.story-text strong{
    font-weight:700;
}

.story-text em{
    font-style:italic;
}

.story-text[data-length="short"]{
    width:min(280px, 46vw);
    font-size:calc(1.3rem * var(--font-scale));
    font-style:italic;
}

.story-text[data-length="medium"]{
    width:min(400px, 42vw);
}

.story-text[data-length="long"]{
    width:min(520px, 46vw);
}

@media (prefers-reduced-motion: reduce){
    .story-node{ transition:none; opacity:1; }
}


/* =========================
   SECTION 3: CREDITS
========================= */

.credits{

    min-height:auto;

    display:flex;

    justify-content:center;
    align-items:center;

    padding:0px 40px 80px 40px;

}

.message{

    max-width:900px;

    width:100%;

    padding:60px;

    background:white;

    border:none;

    border-radius:20px;

    box-shadow:0 5px 20px rgba(0,0,0,.08);

    font-size:1.4rem;

}


/* =========================
   ACCESSIBILITY TOOLBOX
========================= */

.toolbox{

    position:fixed;

    top:120px;
    left:30px;

    z-index:9999;

    display:flex;

    gap:12px;

}

.toolbox button{

    width:48px;
    height:48px;

    border:none;

    background:none;

    padding:0;

    cursor:pointer;

}

.toolbox img{

    width:100%;
    height:100%;

    display:block;

}


/* =========================
   RESPONSIVE
========================= */

@media (max-width:1024px){

    :root{ --overlap:70px; }

    .message{
        padding:40px;
        font-size:1.1rem;
    }

}

@media (max-width:760px){

    :root{ --overlap:0px; --rhythm:36px; --cluster-gap:20px; }

    .story{ padding:80px 20px 120px; }

    .story-node,
    .story-node:nth-child(odd),
    .story-node:nth-child(even){
        max-width:100%;
        align-self:center;
    }

    .story-image.is-portrait,
    .story-image.is-landscape{
        width:min(420px, 84vw);
    }

    .story-text[data-length="short"],
    .story-text[data-length="medium"],
    .story-text[data-length="long"]{
        width:100%;
    }

    .message{
        padding:28px;
        font-size:1rem;
    }

    .toolbox{
        top:auto;
        bottom:20px;
        left:20px;
    }

}