:root {
    --paper: #EEF0EA;
    --panel: #F8F9F4;
    --ink: #171B16;
    --ink-soft: #545C4E;
    --ink-faint: #8B9285;
    --line: #CBD1C0;
    --line-strong: #A6AE97;
    --signal: #2B6E62;
    --signal-soft: #DCE7E1;
    --rust: #A85A2E;
    --rust-soft: #F0DDCB;
    --mono: 'IBM Plex Mono', ui-monospace, SFMono-Regular, Menlo, monospace;
    --sans: 'IBM Plex Sans', -apple-system, BlinkMacSystemFont, sans-serif;
    --rail-w: 34px;
    --maxw: 760px;
}

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

html { scroll-behavior: smooth; }

body {
    font-family: var(--sans);
    background: var(--paper);
    color: var(--ink);
    line-height: 1.65;
    padding-left: var(--rail-w);
}

a { color: inherit; }

::selection { background: var(--signal); color: var(--panel); }

:focus-visible { outline: 2px solid var(--signal); outline-offset: 3px; }

/* Trace rail — same signature element as the homepage */
.trace-rail {
    position: fixed;
    top: 0; left: 0;
    width: var(--rail-w);
    height: 100%;
    background: var(--panel);
    border-right: 1px solid var(--line);
    z-index: 1200;
}

.trace-rail::before {
    content: '';
    position: absolute;
    left: 50%; top: 0; bottom: 0;
    border-left: 1px dashed var(--line-strong);
}

.trace-fill {
    position: absolute;
    left: 50%; top: 0;
    width: 0; height: 0%;
    border-left: 2px solid var(--signal);
    transition: height 0.08s linear;
}

.trace-fill::after {
    content: '';
    position: absolute;
    bottom: -3px; left: -3px;
    width: 7px; height: 7px;
    background: var(--signal);
}

@media (max-width: 860px) {
    body { padding-left: 0; }
    .trace-rail { display: none; }
}

/* Nav */
nav {
    position: fixed;
    top: 0; left: var(--rail-w); right: 0;
    z-index: 1000;
    background: rgba(238, 240, 234, 0.9);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--line);
    transition: border-color 0.2s ease;
}

nav.scrolled { border-bottom-color: var(--line-strong); }

@media (max-width: 860px) { nav { left: 0; } }

.nav-inner {
    max-width: 1120px;
    margin: 0 auto;
    padding: 0 2.25rem;
    height: 58px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    font-family: var(--mono);
}

.nav-logo { font-size: 0.92rem; font-weight: 500; text-decoration: none; color: var(--ink); }
.nav-logo .prompt { color: var(--signal); }

.nav-links { display: flex; list-style: none; gap: 1.5rem; font-size: 0.85rem; }
.nav-links a { text-decoration: none; color: var(--ink-soft); transition: color 0.15s ease; }
.nav-links a:hover { color: var(--signal); }

@media (max-width: 640px) { .nav-links { gap: 0.9rem; font-size: 0.75rem; } }

/* Post header */
.post-head {
    max-width: var(--maxw);
    margin: 0 auto;
    padding: 9rem 2rem 3rem;
}

.doc-path {
    font-family: var(--mono);
    font-size: 0.78rem;
    color: var(--ink-faint);
    margin-bottom: 1rem;
}

.doc-path a { color: var(--signal); text-decoration: none; }
.doc-path a:hover { text-decoration: underline; }

.post-category {
    display: inline-block;
    font-family: var(--mono);
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--rust);
    background: var(--rust-soft);
    border: 1px solid var(--rust-soft);
    padding: 0.25rem 0.55rem;
    margin-bottom: 1.1rem;
}

.post-head h1 {
    font-family: var(--mono);
    font-weight: 600;
    letter-spacing: -0.01em;
    font-size: clamp(1.7rem, 4vw, 2.4rem);
    line-height: 1.15;
    margin-bottom: 1rem;
}

.post-tagline {
    font-size: 1.08rem;
    color: var(--ink-soft);
    margin-bottom: 1.6rem;
    max-width: 58ch;
}

.post-meta {
    display: flex;
    flex-wrap: wrap;
    gap: 1.4rem;
    font-family: var(--mono);
    font-size: 0.8rem;
    color: var(--ink-faint);
    padding-bottom: 1.6rem;
    border-bottom: 1px solid var(--line);
}

.post-meta span { display: inline-flex; align-items: center; gap: 0.4rem; }
.post-meta i { color: var(--signal); }

/* Like widget */
.like-widget { margin-top: 1.6rem; }

.like-btn {
    font-family: var(--mono);
    font-size: 0.85rem;
    display: inline-flex;
    align-items: center;
    gap: 0.55rem;
    padding: 0.55rem 1rem;
    border: 1px solid var(--line-strong);
    background: var(--panel);
    color: var(--ink-soft);
    cursor: pointer;
    transition: border-color 0.15s ease, color 0.15s ease;
}

.like-btn i { color: var(--rust); }

.like-btn:hover { border-color: var(--rust); color: var(--ink); }

.like-btn.liked {
    border-color: var(--rust);
    color: var(--ink);
    background: var(--rust-soft);
}

.like-btn:disabled { opacity: 0.6; cursor: default; }

/* Article body */
.post-body {
    max-width: var(--maxw);
    margin: 0 auto;
    padding: 2.6rem 2rem 5rem;
}

.post-body h2 {
    font-family: var(--mono);
    font-weight: 600;
    font-size: 1.3rem;
    color: var(--ink);
    margin: 2.6rem 0 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid var(--line);
}

.post-body h2:first-child { margin-top: 0; }

.post-body h3 {
    font-family: var(--mono);
    font-weight: 600;
    font-size: 1.05rem;
    color: var(--ink);
    margin: 1.8rem 0 0.7rem;
}

.post-body p {
    font-size: 1.02rem;
    color: var(--ink-soft);
    margin-bottom: 1.3rem;
}

.post-body p strong { color: var(--ink); font-weight: 700; }

.post-body ul, .post-body ol {
    margin: 0 0 1.3rem 1.4rem;
    color: var(--ink-soft);
    font-size: 1rem;
}

.post-body li { margin-bottom: 0.5rem; }
.post-body li strong { color: var(--ink); }

code {
    font-family: var(--mono);
    background: var(--signal-soft);
    color: var(--signal);
    padding: 0.15em 0.4em;
    font-size: 0.88em;
}

pre code, .formula-block {
    display: block;
    font-family: var(--mono);
    padding: 1.1rem 1.4rem;
    background: var(--panel);
    border: 1px solid var(--line-strong);
    border-left: 3px solid var(--signal);
    overflow-x: auto;
    white-space: pre;
    color: var(--ink);
    font-size: 0.88rem;
}

.formula-block { white-space: pre-wrap; margin: 1.5rem 0; }

.abstract {
    background: var(--panel);
    border: 1px solid var(--line-strong);
    padding: 1.6rem 1.8rem;
    margin: 0 0 2.6rem;
}

.abstract-label {
    font-family: var(--mono);
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--signal);
    margin-bottom: 0.7rem;
}

.abstract p { font-size: 1rem; margin-bottom: 0; }

blockquote {
    border-left: 3px solid var(--rust);
    background: var(--panel);
    padding: 1.1rem 1.4rem;
    margin: 1.8rem 0;
    font-style: italic;
    color: var(--ink-soft);
}

blockquote strong { font-style: normal; color: var(--ink); }
blockquote p { margin-bottom: 0; }

.callout {
    background: var(--signal-soft);
    border: 1px solid var(--line-strong);
    padding: 1.4rem 1.7rem;
    margin: 1.8rem 0;
}

.callout-title {
    font-family: var(--mono);
    font-size: 0.75rem;
    font-weight: 600;
    letter-spacing: 0.08em;
    text-transform: uppercase;
    color: var(--signal);
    margin-bottom: 0.7rem;
}

.callout p { margin-bottom: 0; color: var(--ink); font-size: 1rem; }
.callout ul { margin-bottom: 0; }

.callout.gaps { background: var(--rust-soft); }
.callout.gaps .callout-title { color: var(--rust); }

.steps { counter-reset: step; list-style: none; margin: 0 0 1.3rem 0; }

.steps li {
    counter-increment: step;
    display: flex;
    gap: 1.1rem;
    align-items: flex-start;
    margin-bottom: 0.9rem;
    font-size: 1rem;
    color: var(--ink-soft);
}

.steps li::before {
    content: counter(step);
    flex-shrink: 0;
    width: 24px; height: 24px;
    border: 1px solid var(--signal);
    color: var(--signal);
    font-family: var(--mono);
    display: flex; align-items: center; justify-content: center;
    font-size: 0.78rem; font-weight: 600;
    margin-top: 0.1em;
}

.reading-list {
    background: var(--panel);
    border: 1px dashed var(--line-strong);
    padding: 1.7rem 2rem;
    margin: 2.6rem 0;
}

.reading-list h3 {
    font-family: var(--mono);
    font-size: 0.85rem;
    letter-spacing: 0.06em;
    text-transform: uppercase;
    color: var(--ink);
    margin-bottom: 1.1rem;
}

.reading-list ul { list-style: none; margin: 0; color: var(--ink-soft); }
.reading-list li { padding: 0.55rem 0; border-top: 1px solid var(--line); font-size: 0.92rem; }
.reading-list li:first-child { border-top: none; }
.reading-list li strong { color: var(--ink); }
.reading-list li code { background: var(--paper); }

.post-nav {
    border-top: 1px solid var(--line);
    padding: 1.8rem 0 0;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 1rem;
    font-family: var(--mono);
    font-size: 0.85rem;
}

.post-nav a { text-decoration: none; color: var(--signal); display: flex; align-items: center; gap: 0.5rem; }
.post-nav a:hover { text-decoration: underline; }

.disclaimer {
    font-size: 0.88rem;
    color: var(--ink-faint);
    font-style: italic;
    margin-top: 2.6rem;
    padding-top: 1.6rem;
    border-top: 1px dashed var(--line);
}

.disclaimer a { color: var(--signal); }

footer {
    border-top: 1px solid var(--line);
    padding: 2.2rem 2rem;
    text-align: center;
    font-family: var(--mono);
    font-size: 0.78rem;
    color: var(--ink-faint);
}

footer a { color: var(--signal); text-decoration: none; }

@media (max-width: 640px) {
    .post-head { padding: 7.5rem 1.25rem 2rem; }
    .post-body { padding: 2rem 1.25rem 4rem; }
}