/* =========================================================================
   StudyFlix Shared Shell
   -------------------------------------------------------------------------
   ONE quest shell for every studio: same header layout, same stat cluster,
   same tab bar, same button hierarchy. A subject changes only its accent
   colour and its icon set.

   Rationale (design review): the hub, the Rome quest and the Science quest
   read as three products bolted together. Netflix stays recognisable across
   wildly different key art because the CHROME never changes.
   ========================================================================= */

:root {
  /* Neutral shell chrome, identical in every studio. */
  --sf-shell-bg: #101013;
  --sf-shell-bar: #17171c;
  --sf-shell-line: rgba(255, 255, 255, 0.10);
  --sf-shell-text: #f4f4f6;
  --sf-shell-muted: #a1a1aa;

  /* Per-subject accent. Each studio overrides ONLY these two. */
  --sf-accent: #e50914;
  --sf-accent-ink: #ffffff;

  /* Action colours carry a fixed meaning across the whole product.
     "Print" is styled as PAPER rather than as one more accent colour, so it
     stays distinguishable from "play" even in a studio whose accent is amber. */
  --sf-print-paper: #f4efe4;
  --sf-print-ink: #7c4a10;
  --sf-print-edge: #d9b98b;

  --sf-radius: 8px;
  --sf-radius-pill: 999px;
  --sf-ease: cubic-bezier(0.22, 0.61, 0.36, 1);
}

/* Subject accents. The ONLY thing that changes between studios. */
.sf-subject-rome     { --sf-accent: #c8102e; --sf-accent-ink: #ffffff; }
.sf-subject-science  { --sf-accent: #0d9488; --sf-accent-ink: #ffffff; }
.sf-subject-math     { --sf-accent: #6366f1; --sf-accent-ink: #ffffff; }
.sf-subject-grade3   { --sf-accent: #db2777; --sf-accent-ink: #ffffff; }
.sf-subject-calculus { --sf-accent: #2563eb; --sf-accent-ink: #ffffff; }
.sf-subject-coffee   { --sf-accent: #b45309; --sf-accent-ink: #ffffff; }

/* =========================================================================
   ICONS
   ========================================================================= */
.sf-icon {
  display: block;
  flex: 0 0 auto;
  vertical-align: middle;
}

/* The placeholder span that icons.js upgrades. */
[data-sf-icon] {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  line-height: 0;
}

/* =========================================================================
   ACTION BUTTONS — one meaning per colour, everywhere
   -------------------------------------------------------------------------
     .sf-btn--play     accent   start / open the interactive thing
     .sf-btn--explore  neutral  move to another part of the same studio
     .sf-btn--print    amber    produces paper (worksheet, workbook, PDF)
     .sf-btn--info     outline  tells you about something, changes nothing
   ========================================================================= */
.sf-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 20px;
  border: 1px solid transparent;
  border-radius: var(--sf-radius);
  font: inherit;
  font-weight: 700;
  font-size: 0.95rem;
  line-height: 1.2;
  cursor: pointer;
  text-decoration: none;
  transition: background-color 0.18s var(--sf-ease),
              border-color 0.18s var(--sf-ease),
              transform 0.18s var(--sf-ease);
}

.sf-btn:active { transform: translateY(1px); }

.sf-btn:focus-visible {
  outline: 2px solid var(--sf-accent);
  outline-offset: 2px;
}

.sf-btn--play {
  background: var(--sf-accent);
  color: var(--sf-accent-ink);
}
.sf-btn--play:hover { filter: brightness(1.12); }

.sf-btn--explore {
  background: rgba(255, 255, 255, 0.10);
  color: var(--sf-shell-text);
  border-color: rgba(255, 255, 255, 0.18);
}
.sf-btn--explore:hover { background: rgba(255, 255, 255, 0.17); }

/* Paper, with a ruled edge: unmistakably "this produces a printout", and it
   never reads as a second play button whatever the subject accent is. */
.sf-btn--print {
  background: var(--sf-print-paper);
  color: var(--sf-print-ink);
  border-color: var(--sf-print-edge);
  padding-left: 26px;
  position: relative;
  overflow: hidden;
}

.sf-btn--print::before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: 7px;
  background: repeating-linear-gradient(180deg,
    var(--sf-print-paper) 0 7px, var(--sf-print-edge) 7px 9px);
}

.sf-btn--print:hover { background: #ffffff; border-color: #c9a06a; }

.sf-btn--info {
  background: transparent;
  color: var(--sf-shell-muted);
  border-color: rgba(255, 255, 255, 0.22);
}
.sf-btn--info:hover { color: var(--sf-shell-text); border-color: rgba(255, 255, 255, 0.45); }

.sf-btn--sm { padding: 7px 13px; font-size: 0.85rem; }

/* Light-surface studios need readable neutral variants. */
.sf-on-light .sf-btn--explore {
  background: rgba(15, 23, 42, 0.06);
  color: #1e293b;
  border-color: rgba(15, 23, 42, 0.16);
}
.sf-on-light .sf-btn--explore:hover { background: rgba(15, 23, 42, 0.11); }
.sf-on-light .sf-btn--info { color: #475569; border-color: rgba(15, 23, 42, 0.22); }
.sf-on-light .sf-btn--info:hover { color: #0f172a; border-color: rgba(15, 23, 42, 0.45); }

/* =========================================================================
   QUEST SHELL CHROME
   ========================================================================= */
.sf-shell-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  flex-wrap: wrap;
  padding: 12px 24px;
  background: var(--sf-shell-bar);
  border-bottom: 1px solid var(--sf-shell-line);
  color: var(--sf-shell-text);
  position: relative;
}

/* The accent is a hairline, not a whole new visual language. */
.sf-shell-header::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -1px;
  height: 2px;
  background: var(--sf-accent);
}

.sf-shell-left {
  display: flex;
  align-items: center;
  gap: 16px;
  min-width: 0;
}

.sf-back-hub {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 8px 14px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: var(--sf-radius-pill);
  background: rgba(255, 255, 255, 0.06);
  color: var(--sf-shell-text);
  font-size: 0.85rem;
  font-weight: 700;
  text-decoration: none;
  white-space: nowrap;
  cursor: pointer;
  transition: background-color 0.18s var(--sf-ease);
}
.sf-back-hub:hover { background: rgba(255, 255, 255, 0.14); }

.sf-shell-mark {
  display: flex;
  align-items: center;
  gap: 12px;
  min-width: 0;
}

.sf-shell-glyph {
  width: 42px;
  height: 42px;
  flex: 0 0 auto;
  display: grid;
  place-items: center;
  border-radius: 10px;
  background: var(--sf-accent);
  color: var(--sf-accent-ink);
}

.sf-shell-title {
  font-family: 'Montserrat', sans-serif;
  font-size: 1.08rem;
  font-weight: 800;
  letter-spacing: -0.2px;
  color: var(--sf-shell-text);
  margin: 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.sf-shell-sub {
  font-size: 0.76rem;
  color: var(--sf-shell-muted);
  margin: 2px 0 0;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.sf-shell-right {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.sf-stat {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 7px 14px;
  border-radius: var(--sf-radius-pill);
  background: rgba(255, 255, 255, 0.07);
  border: 1px solid var(--sf-shell-line);
  font-size: 0.85rem;
  font-weight: 700;
  color: var(--sf-shell-text);
  white-space: nowrap;
}

.sf-stat .sf-icon { color: var(--sf-accent); }
.sf-stat--xp .sf-icon { color: #fbbf24; }
.sf-stat--streak .sf-icon { color: #fb7185; }
.sf-stat--badges .sf-icon { color: #a3e635; }

.sf-stat-label { color: var(--sf-shell-muted); font-weight: 600; }

.sf-icon-btn {
  width: 38px;
  height: 38px;
  display: grid;
  place-items: center;
  border-radius: var(--sf-radius-pill);
  border: 1px solid var(--sf-shell-line);
  background: rgba(255, 255, 255, 0.07);
  color: var(--sf-shell-text);
  cursor: pointer;
  transition: background-color 0.18s var(--sf-ease);
}
.sf-icon-btn:hover { background: rgba(255, 255, 255, 0.16); }

/* ---- shared tab bar ---- */
.sf-shell-tabs {
  display: flex;
  gap: 4px;
  padding: 0 24px;
  background: var(--sf-shell-bar);
  border-bottom: 1px solid var(--sf-shell-line);
  overflow-x: auto;
  scrollbar-width: none;
}
.sf-shell-tabs::-webkit-scrollbar { display: none; }

.sf-shell-tab {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 13px 16px;
  border: none;
  border-bottom: 3px solid transparent;
  background: none;
  color: var(--sf-shell-muted);
  font: inherit;
  font-weight: 700;
  font-size: 0.88rem;
  white-space: nowrap;
  cursor: pointer;
  transition: color 0.18s var(--sf-ease), border-color 0.18s var(--sf-ease);
}
.sf-shell-tab:hover { color: var(--sf-shell-text); }
.sf-shell-tab.active {
  color: var(--sf-shell-text);
  border-bottom-color: var(--sf-accent);
}
.sf-shell-tab.active .sf-icon { color: var(--sf-accent); }

@media (max-width: 720px) {
  .sf-shell-header { padding: 10px 14px; }
  .sf-shell-sub { display: none; }
  .sf-shell-tabs { padding: 0 10px; }
}

/* Respect a reduced-motion preference across the shared shell. */
@media (prefers-reduced-motion: reduce) {
  .sf-btn, .sf-back-hub, .sf-icon-btn, .sf-shell-tab { transition: none; }
  .sf-btn:active { transform: none; }
}