/* =========================================================================
 * project-nav.css
 *
 * The single navigation component shared by every case-study page
 * (work/tal.html, work/houyi.html). Previously TAL and Houyi each shipped
 * their own bespoke header, which is why they looked and behaved
 * differently. Both now use the identical markup + this stylesheet, so the
 * nav is consistent across the whole portfolio.
 *
 * Behaviour summary
 *  - Desktop (>768px): logo left, project title centre, links inline right.
 *  - Mobile  (<=768px): links collapse into a hamburger; tapping it drops a
 *    full-width panel DOWN from the top of the viewport (never a sideways
 *    slide, which is what the homepage used to do).
 *  - Any page: the bar reveals itself on scroll and fades out ~1.5s after
 *    scrolling stops. See project-nav.js.
 *
 * The component is deliberately namespaced `.proj-nav__*` so it can never
 * collide with Bootstrap's `.nav` / `.navbar` (the old TAL header used
 * those class names and was silently fighting Bootstrap for styles).
 * ========================================================================= */

:root {
  --proj-nav-height: 72px;
  --proj-nav-accent: #254AD4;
  --proj-nav-ink: #333;
  --proj-nav-ease: cubic-bezier(0.22, 0.61, 0.36, 1);
  /* A true ease-out for the departure: fast at first, then a long settle. */
  --proj-nav-ease-out: cubic-bezier(0.16, 1, 0.3, 1);
}

/* -------------------------------------------------------------------------
 * 1. The bar
 * ---------------------------------------------------------------------- */
.proj-nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  height: var(--proj-nav-height);
  padding: 0 32px;
  background: rgba(255, 255, 255, 0.94);
  /* frosted glass so page content reading through the bar stays legible */
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  backdrop-filter: saturate(180%) blur(12px);
  box-shadow: 0 1px 12px rgba(0, 0, 0, 0.09);
  font-family: 'Roboto', 'Quicksand', Arial, sans-serif;
  letter-spacing: 1.6px;

  /* --- show / hide transition ---
     Only transform + opacity are animated: both are compositor-only
     properties, so the motion stays at 60fps and never triggers layout.

     Appearing is quick and snappy (0.28s) — the bar should feel like it's
     already there the moment you reach for it. Leaving is slower and uses
     a pure ease-out (0.55s), so it drifts away rather than snapping out
     of existence. Asymmetric timing like this is what makes an auto-hide
     feel considered instead of twitchy. */
  transform: translateY(0);
  opacity: 1;
  transition: transform 300ms var(--proj-nav-ease-out),
              opacity 300ms var(--proj-nav-ease-out),
              box-shadow 300ms linear,
              background-color 300ms linear;
  will-change: transform, opacity;
}

/* Applied by project-nav.js once scrolling has been idle for ~1.5s. */
.proj-nav.is-hidden {
  transform: translateY(calc(-1 * var(--proj-nav-height) - 20px));
  opacity: 0;
  /* stop the hidden bar swallowing taps meant for the content behind it */
  pointer-events: none;
  transition: transform 300ms var(--proj-nav-ease-out),
              opacity 300ms var(--proj-nav-ease-out),
              box-shadow 300ms linear;
}

/* --- Pinned state (at the top of the page) ---
   At the very top the bar is part of the page rather than something
   floating over it: no shadow, fully opaque, no blur. It only lifts into
   a floating "sheet" once content has scrolled underneath it, which is
   the moment separation actually needs communicating. */
.proj-nav.is-pinned {
  background: #fff;
  -webkit-backdrop-filter: none;
  backdrop-filter: none;
  box-shadow: none;
}

/* -------------------------------------------------------------------------
 * 2. Logo / title / links
 * ---------------------------------------------------------------------- */
.proj-nav__logo {
  display: flex;
  align-items: center;
  flex: 0 0 auto;
  line-height: 0;
}

.proj-nav__logo img {
  width: 44px;
  height: auto;
  transition: opacity 0.25s var(--proj-nav-ease);
}

.proj-nav__logo:hover img {
  opacity: 0.65;
}

/* Centered on the bar itself (not the flex space left between logo and
 * links), so it sits at the true page center even though the logo and
 * links groups are different widths on every page. */
.proj-nav__title {
  position: absolute;
  left: 50%;
  transform: translateX(-50%);
  max-width: 50%;
  text-align: center;
  font-size: 13.6px;
  font-weight: 400;
  letter-spacing: 2.9px;
  text-transform: uppercase;
  color: var(--proj-nav-ink);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.proj-nav__links {
  display: flex;
  align-items: center;
  flex: 0 0 auto;
  gap: 32px;
}

.proj-nav__links a {
  position: relative;
  font-size: 12px;
  font-weight: 400;
  letter-spacing: 2.2px;
  text-transform: uppercase;
  color: var(--proj-nav-ink);
  text-decoration: none;
  padding: 4px 0;
}

/* Underline that wipes in from the left — same affordance the homepage
   sidebar links use, so hover feedback feels like one site. */
.proj-nav__links a::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: 0;
  width: 100%;
  height: 1px;
  background: var(--proj-nav-accent);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform 0.3s var(--proj-nav-ease);
}

.proj-nav__links a:hover,
.proj-nav__links a:focus {
  color: var(--proj-nav-accent);
}

.proj-nav__links a:hover::after,
.proj-nav__links a:focus::after {
  transform: scaleX(1);
}

/* -------------------------------------------------------------------------
 * 3. Hamburger button (hidden on desktop)
 * ---------------------------------------------------------------------- */
.proj-nav__toggle {
  display: none; /* desktop */
  position: relative;
  flex: 0 0 auto;
  width: 44px;   /* 44px is the minimum comfortable touch target */
  height: 44px;
  padding: 0;
  border: 0;
  background: transparent;
  cursor: pointer;
}

/* Three bars built from one span + its two pseudo-elements. */
.proj-nav__toggle span,
.proj-nav__toggle span::before,
.proj-nav__toggle span::after {
  position: absolute;
  left: 50%;
  width: 24px;
  height: 2px;
  margin-left: -12px;
  background: var(--proj-nav-ink);
  transition: transform 0.35s var(--proj-nav-ease),
              opacity 0.2s linear,
              top 0.35s var(--proj-nav-ease);
}

.proj-nav__toggle span {
  top: 50%;
  margin-top: -1px;
}

.proj-nav__toggle span::before,
.proj-nav__toggle span::after {
  content: '';
  margin-left: -12px;
}

.proj-nav__toggle span::before { top: -7px; }
.proj-nav__toggle span::after  { top: 7px; }

/* Hamburger morphs into an X while the panel is open. */
.proj-nav.is-open .proj-nav__toggle span {
  background: transparent;
}

.proj-nav.is-open .proj-nav__toggle span::before {
  top: 0;
  transform: rotate(45deg);
}

.proj-nav.is-open .proj-nav__toggle span::after {
  top: 0;
  transform: rotate(-45deg);
}

/* -------------------------------------------------------------------------
 * 4. Mobile: links become a panel that drops DOWN from the bar
 * ---------------------------------------------------------------------- */
@media screen and (max-width: 768px) {
  .proj-nav {
    --proj-nav-height: 60px;
    padding: 0 16px;
  }

  .proj-nav__toggle {
    display: block;
  }

  .proj-nav__title {
    position: static;
    transform: none;
    max-width: none;
    flex: 1 1 auto;
    text-align: left;
    padding-left: 12px;
    font-size: 11.5px;
    letter-spacing: 1.9px;
  }

  .proj-nav__links {
    /* Anchored to the BOTTOM of the bar and revealed by animating its own
       height, so it unfolds downward over the page instead of sliding in
       from the side. `position: fixed` keeps it pinned even though the bar
       itself may be mid-transform. */
    position: fixed;
    top: var(--proj-nav-height);
    left: 0;
    right: 0;
    display: block;
    padding: 0 24px;
    background: rgba(255, 255, 255, 0.98);
    -webkit-backdrop-filter: saturate(180%) blur(12px);
    backdrop-filter: saturate(180%) blur(12px);
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.08);

    max-height: 0;
    overflow: hidden;
    opacity: 0;
    visibility: hidden;
    transition: max-height 0.4s var(--proj-nav-ease),
                opacity 0.28s var(--proj-nav-ease),
                padding 0.4s var(--proj-nav-ease),
                visibility 0s linear 0.4s;
  }

  .proj-nav.is-open .proj-nav__links {
    max-height: 70vh;
    opacity: 1;
    visibility: visible;
    padding: 8px 24px 24px;
    overflow-y: auto;
    transition: max-height 0.45s var(--proj-nav-ease),
                opacity 0.28s var(--proj-nav-ease) 0.05s,
                padding 0.45s var(--proj-nav-ease),
                visibility 0s linear 0s;
  }

  .proj-nav__links a {
    display: block;
    padding: 16px 0;
    font-size: 14.4px;
    letter-spacing: 2.6px;
    border-bottom: 1px solid rgba(0, 0, 0, 0.07);

    /* Each row lifts into place, staggered by :nth-child below — the panel
       reads as one gesture rather than a block that pops in. */
    opacity: 0;
    transform: translateY(-8px);
    transition: opacity 0.3s var(--proj-nav-ease),
                transform 0.3s var(--proj-nav-ease);
  }

  .proj-nav__links a:last-child {
    border-bottom: 0;
  }

  .proj-nav__links a::after {
    display: none; /* the wipe underline is a hover affordance; no hover here */
  }

  .proj-nav.is-open .proj-nav__links a {
    opacity: 1;
    transform: translateY(0);
  }

  .proj-nav.is-open .proj-nav__links a:nth-child(1) { transition-delay: 0.10s; }
  .proj-nav.is-open .proj-nav__links a:nth-child(2) { transition-delay: 0.16s; }
  .proj-nav.is-open .proj-nav__links a:nth-child(3) { transition-delay: 0.22s; }
  .proj-nav.is-open .proj-nav__links a:nth-child(4) { transition-delay: 0.28s; }
}

/* -------------------------------------------------------------------------
 * 5. Accessibility
 * ---------------------------------------------------------------------- */
.proj-nav a:focus-visible,
.proj-nav button:focus-visible {
  outline: 2px solid var(--proj-nav-accent);
  outline-offset: 3px;
}

/* Respect the OS "reduce motion" setting: the nav still shows and hides,
   it just does so instantly rather than sliding. */
@media (prefers-reduced-motion: reduce) {
  .proj-nav,
  .proj-nav__links,
  .proj-nav__links a,
  .proj-nav__toggle span,
  .proj-nav__toggle span::before,
  .proj-nav__toggle span::after {
    transition-duration: 0.01ms !important;
    transition-delay: 0ms !important;
  }
}