/* ============================================================
   Shared sketchbook theme for the interactive Chinese lessons
   Plain CSS — no build step, works over file://
   ============================================================ */

:root {
  --paper: #b0c6b3;
  --paper-light: #c2d4c4;
  --paper-dark: #9db8a1;
  --ink: #16150f;
  --ink-soft: #3c3a30;
  --ink-mute: #5d5b4d;
  --cinnabar: #db3356;
  --cinnabar-dark: #b81f42;
  --jade: #33523f;
  --jade-light: #4c7359;
  --mustard: #d9a441;
  --cream: #f4efe4;
  --tone1: #c0392b;
  --tone2: #d68910;
  --tone3: #1e7d4f;
  --tone4: #2471a3;
  --tone0: #7a7869;
  --shadow: 4px 4px 0 0 var(--ink);
  --shadow-sm: 2px 2px 0 0 var(--ink);
  --shadow-lg: 7px 7px 0 0 var(--ink);
  --font-song: Georgia, "Times New Roman", "Songti SC", STSong, SimSun, "Noto Serif CJK SC", serif;
  --font-body: Inter, -apple-system, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--font-body);
  color: var(--ink);
  background-color: var(--paper);
  background-image:
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='196' height='196'%3E%3Cline x1='0.5' y1='0' x2='0.5' y2='196' stroke='%2316150f' stroke-opacity='0.14' stroke-dasharray='1,5'/%3E%3Cline x1='0' y1='0.5' x2='196' y2='0.5' stroke='%2316150f' stroke-opacity='0.07' stroke-dasharray='1,5'/%3E%3C/svg%3E"),
    url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='240' height='240'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2'/%3E%3CfeColorMatrix values='0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.035 0'/%3E%3C/filter%3E%3Crect width='240' height='240' filter='url(%23n)'/%3E%3C/svg%3E");
  line-height: 1.5;
}

::selection { background: var(--cinnabar); color: var(--cream); }
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: rgba(22,21,15,.55); border-radius: 10px; }
::-webkit-scrollbar-thumb:hover { background: rgba(22,21,15,.8); }

button { font-family: var(--font-body); cursor: pointer; }

/* ---------- layout ---------- */
.wrap { max-width: 1100px; margin: 0 auto; padding: 28px 18px 60px; }
@media (min-width: 1024px) { .wrap { padding-left: 46px; } }

.binder-holes {
  position: fixed; left: 8px; top: 0; height: 100%; width: 24px; z-index: 0; pointer-events: none;
  background-image: radial-gradient(circle at center, #16150f 0 7px, rgba(0,0,0,.25) 7.5px 8.5px, transparent 9px);
  background-size: 22px 110px; background-repeat: repeat-y; background-position: center 26px;
  display: none;
}
@media (min-width: 1024px) { .binder-holes { display: block; } }

/* ---------- top nav ---------- */
.topnav {
  position: sticky; top: 0; z-index: 20;
  background: rgba(22,21,15,.96);
  border-bottom: 2px solid var(--ink);
}
.topnav-inner { max-width: 1100px; margin: 0 auto; padding: 12px 16px; display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 8px; }
.brand { background: none; border: 0; text-align: left; display: flex; align-items: baseline; gap: 8px; }
.brand .zh { font-family: var(--font-song); font-size: 24px; font-weight: 900; color: var(--paper-light); }
.brand .en { font-size: 11px; letter-spacing: .22em; text-transform: uppercase; font-weight: 700; color: var(--paper-dark); display: none; }
@media (min-width: 640px) { .brand .en { display: inline; } }
.navbtns { display: flex; flex-wrap: wrap; gap: 4px; }
.navbtns button {
  border: 0; border-radius: 8px; padding: 7px 10px; font-size: 12px; font-weight: 700;
  background: transparent; color: rgba(194,212,196,.85); transition: background .15s;
}
.navbtns button .en { display: none; margin-left: 4px; font-size: 10px; letter-spacing: .12em; text-transform: uppercase; }
@media (min-width: 800px) { .navbtns button .en { display: inline; } }
.navbtns button:hover { background: rgba(194,212,196,.15); }
.navbtns button.active { background: var(--cinnabar); color: var(--cream); }

/* ---------- shared bits ---------- */
.spec-label { font-size: 11px; letter-spacing: .22em; text-transform: uppercase; font-weight: 700; }

.card { background: var(--paper-light); border: 2px solid var(--ink); box-shadow: var(--shadow); border-radius: 14px; }
.card-sm { background: var(--paper-light); border: 2px solid var(--ink); box-shadow: var(--shadow-sm); border-radius: 12px; }

.btn {
  display: inline-flex; align-items: center; gap: 6px;
  border: 2px solid var(--ink); border-radius: 9px; box-shadow: var(--shadow-sm);
  background: var(--cream); color: var(--ink); font-weight: 700;
  padding: 6px 10px; font-size: 12px; transition: transform .12s;
}
.btn:hover { transform: translateY(-2px); }
.btn:active { transform: translateY(0); }
.btn.primary { background: var(--cinnabar); color: var(--cream); }
.btn.jade { background: var(--jade); color: var(--cream); }
.btn.icon { padding: 6px; }
.btn:disabled { opacity: .4; transform: none; cursor: default; }

/* audio speed buttons */
.abtns { display: inline-flex; gap: 6px; align-items: center; }
.abtn {
  display: inline-flex; align-items: center; gap: 4px;
  border: 2px solid var(--ink); border-radius: 8px; box-shadow: var(--shadow-sm);
  background: var(--cream); color: var(--ink); font-weight: 700; font-size: 11px;
  padding: 4px 7px; text-transform: uppercase; letter-spacing: .05em; transition: transform .12s, background .12s;
}
.abtn:hover { transform: translateY(-2px); }
.abtn svg { width: 14px; height: 14px; }
.abtn.slow:hover, .abtn.slow.on { background: var(--mustard); }
.abtn.norm:hover, .abtn.norm.on { background: var(--cinnabar); color: var(--cream); }
.abtn.fast:hover, .abtn.fast.on { background: var(--jade-light); color: var(--cream); }
.abtn.on { animation: pulse-ring 1s ease-out infinite; }
.abtn.small { padding: 3px 5px; font-size: 9px; }
.abtn.small svg { width: 12px; height: 12px; }
.abtn.small .lbl { display: none; }

/* section header */
.sec-head { margin-bottom: 30px; }
.sec-head .row { display: flex; align-items: baseline; gap: 12px; flex-wrap: wrap; }
.sec-head .idx { color: var(--cinnabar); }
.sec-head h2 { font-family: var(--font-song); font-size: 42px; font-weight: 900; margin: 0; }
@media (min-width: 640px) { .sec-head h2 { font-size: 52px; } }
.sec-head .en { color: var(--ink-soft); }
.sec-head .bar { height: 3px; width: 90px; background: var(--ink); margin-top: 12px; }
.sec-head p { margin-top: 12px; max-width: 640px; font-size: 14px; color: var(--ink-soft); }

/* grids */
.grid { display: grid; gap: 20px; }
.grid.cols-2 { grid-template-columns: 1fr; }
.grid.cols-3 { grid-template-columns: 1fr; }
.grid.cols-4 { grid-template-columns: repeat(2,1fr); }
@media (min-width: 640px) { .grid.cols-2 { grid-template-columns: repeat(2,1fr); } .grid.cols-3 { grid-template-columns: repeat(2,1fr); } .grid.cols-4 { grid-template-columns: repeat(3,1fr); } }
@media (min-width: 900px) { .grid.cols-3 { grid-template-columns: repeat(3,1fr); } .grid.cols-4 { grid-template-columns: repeat(4,1fr); } }

/* tone colors */
.t1 { color: var(--tone1); } .t2 { color: var(--tone2); } .t3 { color: var(--tone3); } .t4 { color: var(--tone4); } .t0 { color: var(--tone0); }

/* hero chars entrance */
@keyframes heroChar { 0%{opacity:0;transform:translateY(40px) rotate(6deg) scale(.85);} 100%{opacity:1;transform:translateY(0) rotate(0) scale(1);} }
.hero-char { animation: heroChar .7s cubic-bezier(.2,.7,.3,1) both; display: inline-block; }

/* flip card */
.flip-scene { perspective: 1200px; cursor: pointer; }
.flip-inner { position: relative; width: 100%; height: 100%; transform-style: preserve-3d; transition: transform .55s cubic-bezier(.2,.7,.3,1); }
.flip-inner.flipped { transform: rotateY(180deg); }
.flip-face { position: absolute; inset: 0; backface-visibility: hidden; -webkit-backface-visibility: hidden; border-radius: 14px; }
.flip-back { transform: rotateY(180deg); }

/* animations */
@keyframes rise { 0%{transform:translateY(28px);opacity:0;} 100%{transform:translateY(0);opacity:1;} }
.anim-rise { animation: rise .55s cubic-bezier(.2,.7,.3,1) both; }
@keyframes pop { 0%{transform:scale(.6);opacity:0;} 70%{transform:scale(1.08);} 100%{transform:scale(1);opacity:1;} }
.anim-pop { animation: pop .3s cubic-bezier(.2,.7,.3,1) both; }
@keyframes shake { 0%,100%{transform:translateX(0);} 20%,60%{transform:translateX(-7px);} 40%,80%{transform:translateX(7px);} }
.anim-shake { animation: shake .4s ease-in-out; }
@keyframes pulse-ring { 0%{box-shadow:0 0 0 0 rgba(219,51,86,.45);} 100%{box-shadow:0 0 0 14px rgba(219,51,86,0);} }

/* footer */
.foot { border-top: 2px solid rgba(22,21,15,.3); padding: 24px 16px; text-align: center; position: relative; z-index: 1; }
.foot .a { color: var(--ink-mute); }
.foot .b { margin-top: 4px; font-size: 12px; color: var(--ink-mute); }

/* misc helpers */
.mut { color: var(--ink-mute); }
.soft { color: var(--ink-soft); }
.cin { color: var(--cinnabar); }
.jadet { color: var(--jade); }
.center { text-align: center; }
.mt1 { margin-top: 8px; } .mt2 { margin-top: 16px; } .mt3 { margin-top: 28px; } .mt4 { margin-top: 44px; }
.hidden { display: none !important; }

/* back-to-home link */
.homelink { flex-shrink: 0; font-size: 11px; font-weight: 700; text-transform: uppercase; letter-spacing: .1em; color: var(--paper-light); text-decoration: none; border: 2px solid rgba(194,212,196,.5); border-radius: 8px; padding: 5px 10px; transition: all .15s; }
.homelink:hover { background: var(--cream); color: var(--ink); border-color: var(--cream); }
@media (max-width: 900px) { .homelink { order: 3; margin-left: auto; } }

@media (prefers-reduced-motion: reduce) { .anim-rise { animation: none; } }