/* =================================================================
   styles.css  —  the single stylesheet for the whole site
   -----------------------------------------------------------------
   How this file is organised (skim the headings to find things):
     1. Design tokens (CSS variables: colours, spacing, type)
     2. Dark-theme token overrides
     3. Base / reset
     4. Layout helpers (container, section, grid)
     5. Header & navigation
     6. Buttons, tags, badges
     7. Cards (project gallery)
     8. Home / About
     9. Project detail page
    10. Resume page
    11. Contact page
    12. Footer
    13. Lightbox (image zoom)
    14. Utilities & accessibility
    15. Responsive tweaks

   WHY CSS VARIABLES?  Every colour and size lives in one place at the
   top (":root"). Change a value there and it updates everywhere. The
   dark theme simply re-defines those same variables, so we never have
   to write two copies of every rule.
   ================================================================= */

/* ---------- 1. DESIGN TOKENS -------------------------------------
   Colour system (light theme):
   A calm, professional "engineering paper + blueprint" palette.
   - Neutrals are cool greys (slate) so the site reads as precise and
     technical rather than warm/playful.
   - A single blue accent does all the "interactive" work (links,
     buttons, focus rings). One accent keeps the design disciplined.
   Type system:
   - A native system-font stack. It looks great on every OS, loads
     instantly (zero network requests), and never blocks rendering.
     This directly serves the "fast loading / minimal dependencies"
     goal. If you later want a branded font, self-host it and swap the
     --font-sans value.
------------------------------------------------------------------ */
:root {
  /* Brand / accent */
  --accent:        #2563eb;   /* blue-600  — primary actions, links */
  --accent-hover:  #1d4ed8;   /* blue-700  — hover/active */
  --accent-soft:   #eff6ff;   /* blue-50   — tinted backgrounds */
  --accent-ring:   rgba(37, 99, 235, 0.40); /* focus outline colour */

  /* Neutrals (slate) */
  --bg:            #ffffff;    /* page background */
  --bg-subtle:     #f8fafc;    /* alternating sections, code areas */
  --surface:       #ffffff;    /* cards, header */
  --surface-2:     #f1f5f9;    /* chips, secondary surfaces */
  --ink:           #0f172a;    /* primary text (slate-900) */
  --ink-soft:      #334155;    /* body text (slate-700) */
  --muted:         #64748b;    /* secondary text (slate-500) */
  --border:        #e2e8f0;    /* hairline borders (slate-200) */
  --border-strong: #cbd5e1;    /* slate-300 */

  /* Status colour used for the "SOLIDWORKS / Ansys" download groups */
  --solidworks:    #c2410c;    /* warm orange-ish, nods to SW branding */
  --ansys:         #b45309;    /* amber, nods to Ansys branding */
  --other:         #475569;    /* neutral slate */

  /* Spacing scale (rem). Consistent rhythm across the whole site. */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;
  --space-8: 4rem;
  --space-9: 6rem;

  /* Shape & depth */
  --radius:    12px;
  --radius-sm: 8px;
  --radius-lg: 18px;
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 4px 16px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 12px 40px rgba(15, 23, 42, 0.14);

  /* Typography */
  --font-sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue",
               Arial, "Noto Sans", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas,
               "Liberation Mono", monospace;

  --maxw:      1120px;   /* overall page width */
  --maxw-prose: 70ch;    /* comfortable reading measure for long text */

  color-scheme: light;
}

/* ---------- 2. DARK THEME ----------------------------------------
   We support dark mode two ways:
   (a) Automatically, if the visitor's device prefers dark, AND
   (b) Manually, via the moon/sun toggle in the header, which sets
       data-theme="dark" or "light" on <html> and saves the choice.
   Both routes just re-point the same variables below. Because the
   manual toggle uses data-theme, it always wins over the OS setting.
------------------------------------------------------------------ */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --accent:        #60a5fa;  /* blue-400, brighter for dark bg */
    --accent-hover:  #93c5fd;
    --accent-soft:   #172554;
    --accent-ring:   rgba(96, 165, 250, 0.45);

    --bg:            #0b1120;
    --bg-subtle:     #0f172a;
    --surface:       #111c33;
    --surface-2:     #1e293b;
    --ink:           #e8eef9;
    --ink-soft:      #cbd5e1;
    --muted:         #94a3b8;
    --border:        #233047;
    --border-strong: #334155;

    --solidworks:    #fb923c;
    --ansys:         #fbbf24;
    --other:         #94a3b8;

    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.5);
    --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.6);

    color-scheme: dark;
  }
}

/* Manual override: when the user clicks the toggle, <html data-theme="dark"> */
:root[data-theme="dark"] {
  --accent:        #60a5fa;
  --accent-hover:  #93c5fd;
  --accent-soft:   #172554;
  --accent-ring:   rgba(96, 165, 250, 0.45);

  --bg:            #0b1120;
  --bg-subtle:     #0f172a;
  --surface:       #111c33;
  --surface-2:     #1e293b;
  --ink:           #e8eef9;
  --ink-soft:      #cbd5e1;
  --muted:         #94a3b8;
  --border:        #233047;
  --border-strong: #334155;

  --solidworks:    #fb923c;
  --ansys:         #fbbf24;
  --other:         #94a3b8;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.5);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, 0.6);

  color-scheme: dark;
}

/* ---------- 3. BASE / RESET -------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

/* Respect users who ask for less motion (accessibility). */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    transition-duration: 0.001ms !important;
  }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink-soft);
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  /* Fade the page in once CSS is ready (set by main.js adding .ready). */
  transition: background-color 0.2s ease, color 0.2s ease;
}

h1, h2, h3, h4 {
  color: var(--ink);
  line-height: 1.2;
  letter-spacing: -0.015em;
  margin: 0 0 var(--space-4);
  font-weight: 700;
}
h1 { font-size: clamp(2rem, 5vw, 3rem); }
h2 { font-size: clamp(1.5rem, 3.5vw, 2rem); }
h3 { font-size: 1.25rem; }

p  { margin: 0 0 var(--space-4); }

a {
  color: var(--accent);
  text-decoration: none;
}
a:hover { color: var(--accent-hover); text-decoration: underline; }

img, svg, model-viewer { max-width: 100%; display: block; }

ul, ol { margin: 0 0 var(--space-4); padding-left: 1.25rem; }
li { margin-bottom: var(--space-2); }

hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: var(--space-6) 0;
}

code, kbd {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: var(--surface-2);
  padding: 0.1em 0.4em;
  border-radius: 6px;
}

/* ---------- 4. LAYOUT HELPERS ------------------------------------ */
.container {
  width: 100%;
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: var(--space-5);
}

/* A vertical-rhythm section. Alternate background with .section--subtle */
.section { padding-block: var(--space-8); }
.section--subtle { background: var(--bg-subtle); }

.section__head {
  max-width: var(--maxw-prose);
  margin-bottom: var(--space-6);
}
.section__head .eyebrow { margin-bottom: var(--space-2); }
.section__head p { color: var(--muted); font-size: 1.05rem; }

/* Small uppercase label above a heading */
.eyebrow {
  display: inline-block;
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin: 0;
}

/* Responsive auto-fill grid used by the project gallery */
.grid {
  display: grid;
  gap: var(--space-5);
  grid-template-columns: repeat(auto-fill, minmax(min(100%, 320px), 1fr));
}

/* ---------- 5. HEADER & NAVIGATION ------------------------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
  backdrop-filter: saturate(140%) blur(10px);
  border-bottom: 1px solid var(--border);
}
.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  min-height: 64px;
}

/* Wordmark / logo */
.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  font-weight: 800;
  letter-spacing: -0.02em;
  color: var(--ink);
  font-size: 1.05rem;
}
.brand:hover { text-decoration: none; color: var(--ink); }
.brand__mark {
  display: grid;
  place-items: center;
  width: 34px; height: 34px;
  border-radius: 9px;
  background: var(--accent);
  color: #fff;
  font-size: 0.85rem;
  font-weight: 800;
  letter-spacing: 0;
}

/* The nav links + controls cluster */
.nav { display: flex; align-items: center; gap: var(--space-2); }
.nav__links {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  list-style: none;
  margin: 0; padding: 0;
}
.nav__links a {
  display: inline-block;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-sm);
  color: var(--ink-soft);
  font-weight: 600;
  font-size: 0.95rem;
}
.nav__links a:hover { background: var(--surface-2); color: var(--ink); text-decoration: none; }
/* The JS in main.js adds aria-current="page" to the active link */
.nav__links a[aria-current="page"] { color: var(--accent); background: var(--accent-soft); }

/* Icon buttons (theme toggle, hamburger) */
.icon-btn {
  display: inline-grid;
  place-items: center;
  width: 40px; height: 40px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--ink);
  border-radius: var(--radius-sm);
  cursor: pointer;
}
.icon-btn:hover { background: var(--surface-2); }
.icon-btn svg { width: 20px; height: 20px; }

/* Theme toggle shows one icon at a time depending on the theme */
.theme-toggle .icon-sun  { display: none; }
:root[data-theme="dark"] .theme-toggle .icon-sun  { display: block; }
:root[data-theme="dark"] .theme-toggle .icon-moon { display: none; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .theme-toggle .icon-sun  { display: block; }
  :root:not([data-theme="light"]) .theme-toggle .icon-moon { display: none; }
}

/* Hamburger only appears on small screens (see responsive section) */
.nav__toggle { display: none; }

/* ---------- 6. BUTTONS, TAGS, BADGES ----------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: 0.7rem 1.1rem;
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  font: inherit;
  font-weight: 600;
  font-size: 0.95rem;
  cursor: pointer;
  transition: transform 0.05s ease, background-color 0.15s ease, box-shadow 0.15s ease;
  text-decoration: none;
  line-height: 1.2;
}
.btn:hover { text-decoration: none; }
.btn:active { transform: translateY(1px); }

.btn--primary { background: var(--accent); color: #fff; box-shadow: var(--shadow-sm); }
.btn--primary:hover { background: var(--accent-hover); color: #fff; }

.btn--ghost { background: transparent; color: var(--ink); border-color: var(--border-strong); }
.btn--ghost:hover { background: var(--surface-2); color: var(--ink); }

.btn--block { width: 100%; justify-content: flex-start; }
.btn svg { width: 18px; height: 18px; flex: none; }

/* Tag chips used on cards and detail pages */
.tags { display: flex; flex-wrap: wrap; gap: var(--space-2); list-style: none; margin: 0; padding: 0; }
.tag {
  display: inline-block;
  padding: 0.25rem 0.6rem;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--muted);
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 999px;
  white-space: nowrap;
}
.tag--accent { color: var(--accent); background: var(--accent-soft); border-color: transparent; }

/* ---------- 7. CARDS (project gallery) --------------------------- */
.card {
  display: flex;
  flex-direction: column;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  box-shadow: var(--shadow-sm);
  transition: transform 0.15s ease, box-shadow 0.15s ease, border-color 0.15s ease;
}
.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  border-color: var(--border-strong);
}
/* The whole card is a link; this makes the title look like a heading */
.card a { color: inherit; }
.card a:hover { text-decoration: none; }

.card__media {
  aspect-ratio: 16 / 10;
  background: var(--surface-2);
  border-bottom: 1px solid var(--border);
  overflow: hidden;
}
.card__media img { width: 100%; height: 100%; object-fit: cover; }

.card__body { padding: var(--space-5); display: flex; flex-direction: column; gap: var(--space-3); flex: 1; }
.card__title { font-size: 1.15rem; margin: 0; }
.card__summary { color: var(--muted); font-size: 0.95rem; margin: 0; flex: 1; }
.card__footer { margin-top: var(--space-2); }

/* ---------- 8. HOME / ABOUT -------------------------------------- */
.hero { padding-block: var(--space-9) var(--space-8); }
.hero__grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr;
  gap: var(--space-8);
  align-items: center;
}
.hero h1 { margin-bottom: var(--space-4); }
.hero__lead { font-size: 1.2rem; color: var(--ink-soft); max-width: 52ch; }
.hero__cta { display: flex; flex-wrap: wrap; gap: var(--space-3); margin-top: var(--space-5); }

/* Portrait / monogram block on the right of the hero */
.hero__portrait {
  aspect-ratio: 1;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  background: var(--surface-2);
  box-shadow: var(--shadow-md);
  overflow: hidden;
}
.hero__portrait img { width: 100%; height: 100%; object-fit: cover; }

/* "At a glance" fact strip */
.facts { display: grid; grid-template-columns: repeat(auto-fit, minmax(160px, 1fr)); gap: var(--space-4); }
.fact {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: var(--space-5);
}
.fact dt { font-size: 0.8rem; text-transform: uppercase; letter-spacing: 0.06em; color: var(--muted); margin-bottom: var(--space-1); }
.fact dd { margin: 0; font-weight: 700; color: var(--ink); font-size: 1.05rem; }

/* Skill pill groups on the About area */
.skills { display: grid; gap: var(--space-5); }
.skill-group h3 { font-size: 1rem; margin-bottom: var(--space-3); color: var(--ink); }

/* ---------- 9. PROJECT DETAIL PAGE ------------------------------- */
.detail__back { display: inline-flex; align-items: center; gap: var(--space-2); color: var(--muted); font-weight: 600; margin-bottom: var(--space-5); }

.detail__header { max-width: var(--maxw-prose); }
.detail__meta { display: flex; flex-wrap: wrap; gap: var(--space-4); color: var(--muted); font-size: 0.92rem; margin-bottom: var(--space-4); }
.detail__meta span { display: inline-flex; align-items: center; gap: var(--space-2); }

/* Two-column layout: content on the left, sticky downloads on the right */
.detail__layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: var(--space-7);
  align-items: start;
  margin-top: var(--space-6);
}
.detail__content { min-width: 0; }      /* min-width:0 lets long equations scroll instead of overflowing */
.detail__content > section { margin-bottom: var(--space-7); }
.detail__content h2 { padding-bottom: var(--space-2); border-bottom: 1px solid var(--border); }
.prose { max-width: var(--maxw-prose); }
.prose p { color: var(--ink-soft); }

/* Design-decision list: a "decision -> why" pattern */
.decisions { list-style: none; padding: 0; margin: 0; display: grid; gap: var(--space-4); }
.decisions li {
  margin: 0;
  padding: var(--space-5);
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: var(--radius);
}
.decisions .decision { font-weight: 700; color: var(--ink); display: block; margin-bottom: var(--space-2); }
.decisions .rationale { color: var(--ink-soft); margin: 0; }

/* Calculation blocks (KaTeX renders inside .calc__eq / .calc__result) */
.calc {
  padding: var(--space-5);
  background: var(--bg-subtle);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: var(--space-4);
}
.calc__title { font-size: 1.05rem; margin-bottom: var(--space-2); }
.calc__desc { color: var(--ink-soft); margin-bottom: var(--space-3); }
/* Equations can be wide; let them scroll horizontally on small screens */
.calc__eq, .calc__result {
  overflow-x: auto;
  overflow-y: hidden;
  padding: var(--space-3) 0;
}
.calc__result {
  border-top: 1px dashed var(--border-strong);
  margin-top: var(--space-2);
}
.calc__note { font-size: 0.9rem; color: var(--muted); margin: var(--space-2) 0 0; }

/* Image gallery on the detail page */
.gallery { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: var(--space-4); }
.gallery figure { margin: 0; }
.gallery img {
  width: 100%;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  cursor: zoom-in;
  background: var(--surface-2);
}
.gallery figcaption { font-size: 0.88rem; color: var(--muted); margin-top: var(--space-2); }

/* 3D viewer */
model-viewer {
  width: 100%;
  height: 420px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  --poster-color: transparent;
}

/* Sticky downloads sidebar */
.downloads { position: sticky; top: 84px; }
.downloads__card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: var(--space-5);
  box-shadow: var(--shadow-sm);
}
.downloads__card h2 { font-size: 1.1rem; border: none; padding: 0; margin-bottom: var(--space-2); }
.downloads__group { margin-top: var(--space-4); }
.downloads__group-label {
  display: inline-flex; align-items: center; gap: var(--space-2);
  font-size: 0.78rem; font-weight: 700; text-transform: uppercase; letter-spacing: 0.06em;
  margin-bottom: var(--space-2);
}
.downloads__group-label .dot { width: 9px; height: 9px; border-radius: 50%; }
.downloads__group--solidworks .dot { background: var(--solidworks); }
.downloads__group--solidworks .downloads__group-label { color: var(--solidworks); }
.downloads__group--ansys .dot { background: var(--ansys); }
.downloads__group--ansys .downloads__group-label { color: var(--ansys); }
.downloads__group--other .dot { background: var(--other); }
.downloads__group--other .downloads__group-label { color: var(--other); }

/* One download button */
.dl {
  display: flex; align-items: center; gap: var(--space-3);
  width: 100%;
  text-align: left;
  padding: var(--space-3);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface);
  color: var(--ink);
  margin-bottom: var(--space-2);
}
.dl:hover { border-color: var(--accent); background: var(--accent-soft); text-decoration: none; color: var(--ink); }
.dl__icon { flex: none; width: 34px; height: 34px; display: grid; place-items: center; border-radius: 8px; background: var(--surface-2); }
.dl__icon svg { width: 18px; height: 18px; }
.dl__text { min-width: 0; }
.dl__label { display: block; font-weight: 600; font-size: 0.9rem; line-height: 1.3; overflow-wrap: anywhere; }
.dl__size { display: block; font-size: 0.8rem; color: var(--muted); }

/* ---------- 10. RESUME PAGE -------------------------------------- */
.resume__head { display: flex; flex-wrap: wrap; gap: var(--space-4); align-items: center; justify-content: space-between; }
.resume-grid { display: grid; grid-template-columns: 1fr; gap: var(--space-6); }
.entry { margin-bottom: var(--space-5); }
.entry__row { display: flex; flex-wrap: wrap; justify-content: space-between; gap: var(--space-2); }
.entry__title { font-weight: 700; color: var(--ink); }
.entry__meta { color: var(--muted); font-size: 0.92rem; }
.entry__sub { color: var(--ink-soft); font-style: italic; margin-bottom: var(--space-2); }

/* ---------- 11. CONTACT PAGE ------------------------------------- */
.contact-grid { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-7); align-items: start; }
.contact-list { list-style: none; padding: 0; margin: 0; display: grid; gap: var(--space-3); }
.contact-list a, .contact-list span { display: inline-flex; align-items: center; gap: var(--space-3); }
.contact-list svg { width: 20px; height: 20px; color: var(--accent); flex: none; }

/* Optional contact form (Formspree). Hidden by default until you set it up. */
.form-field { display: grid; gap: var(--space-2); margin-bottom: var(--space-4); }
.form-field label { font-weight: 600; color: var(--ink); font-size: 0.95rem; }
.form-field input, .form-field textarea {
  width: 100%;
  padding: 0.7rem 0.85rem;
  font: inherit;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
}
.form-field input:focus, .form-field textarea:focus {
  outline: 3px solid var(--accent-ring);
  outline-offset: 1px;
  border-color: var(--accent);
}

/* ---------- 12. FOOTER ------------------------------------------- */
.site-footer {
  border-top: 1px solid var(--border);
  background: var(--bg-subtle);
  margin-top: var(--space-9);
  padding-block: var(--space-7);
}
.site-footer__inner { display: flex; flex-wrap: wrap; gap: var(--space-4); justify-content: space-between; align-items: center; }
.site-footer small { color: var(--muted); }
.site-footer .social { display: flex; gap: var(--space-3); }
.site-footer .social a { color: var(--muted); }
.site-footer .social a:hover { color: var(--accent); }
.site-footer .social svg { width: 22px; height: 22px; }

/* ---------- 13. LIGHTBOX (image zoom) ---------------------------- */
.lightbox {
  position: fixed; inset: 0; z-index: 100;
  display: none;
  place-items: center;
  padding: var(--space-5);
  background: rgba(2, 6, 23, 0.82);
  backdrop-filter: blur(2px);
}
.lightbox[open], .lightbox.is-open { display: grid; }
.lightbox img { max-width: 92vw; max-height: 86vh; border-radius: var(--radius); box-shadow: var(--shadow-lg); }
.lightbox__close {
  position: absolute; top: var(--space-5); right: var(--space-5);
  width: 44px; height: 44px;
  border: none; border-radius: 50%;
  background: rgba(255,255,255,0.12); color: #fff;
  font-size: 1.5rem; cursor: pointer;
}
.lightbox__close:hover { background: rgba(255,255,255,0.25); }

/* ---------- 14. UTILITIES & ACCESSIBILITY ------------------------ */
/* Visually hidden but available to screen readers */
.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* "Skip to content" link — appears when keyboard-focused */
.skip-link {
  position: absolute; left: var(--space-4); top: -60px;
  z-index: 200;
  background: var(--accent); color: #fff;
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-sm);
  transition: top 0.15s ease;
}
.skip-link:focus { top: var(--space-4); text-decoration: none; }

/* A single, consistent, highly-visible focus ring everywhere.
   Using :focus-visible means it only shows for keyboard users, not
   on mouse clicks — best of both worlds. */
:focus-visible {
  outline: 3px solid var(--accent-ring);
  outline-offset: 2px;
  border-radius: 4px;
}

.text-muted { color: var(--muted); }
.center { text-align: center; }
.mt-0 { margin-top: 0; }
.stack > * + * { margin-top: var(--space-4); }

/* Loading / empty / error states for JS-rendered areas */
.state {
  text-align: center;
  padding: var(--space-8) var(--space-5);
  color: var(--muted);
}
.state--error { color: var(--ink-soft); }

/* ---------- 15. RESPONSIVE --------------------------------------- */
@media (max-width: 880px) {
  .hero__grid { grid-template-columns: 1fr; }
  .hero__portrait { max-width: 320px; order: -1; }   /* portrait first on mobile */
  .detail__layout { grid-template-columns: 1fr; }
  .downloads { position: static; }
  .contact-grid { grid-template-columns: 1fr; }
}

@media (max-width: 720px) {
  /* Turn the nav links into a slide-down panel toggled by the hamburger. */
  .nav__toggle { display: inline-grid; }

  .nav__links {
    position: absolute;
    top: 64px; left: 0; right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-1);
    background: var(--surface);
    border-bottom: 1px solid var(--border);
    box-shadow: var(--shadow-md);
    padding: var(--space-3);
    /* Hidden until JS toggles .is-open (and aria-expanded on the button). */
    display: none;
  }
  .nav__links.is-open { display: flex; }
  .nav__links a { padding: var(--space-3); }
}