:root{
  --navy:#101b38;
  --blue:#2f49df;
  --blue2:#5166f6;
  --gold:#eab84c;
  --ink:#1b2842;
  --muted:#667590;
  --bg:#f3f5fa;
  --line:#e1e6f0;
  --green:#1f7d57;
  --light:#f0d9b5;
  --dark:#b58863;
  --panel:#ffffff;
  --shadow:0 10px 30px rgba(16,27,56,.08);
  --radius:18px;
}
*{box-sizing:border-box}
html,body{margin:0;padding:0}
body{
  font-family:Inter,system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;
  background:var(--bg);
  color:var(--ink);
  -webkit-font-smoothing:antialiased;
  -moz-osx-font-smoothing:grayscale;
}
button,input,select{font:inherit}
button{cursor:pointer;touch-action:manipulation}
button:disabled{opacity:.48;cursor:not-allowed}
.hidden{display:none!important}
.error{font-size:12px;color:#b42238;min-height:12px}

.app{max-width:1180px;margin:0 auto;padding:0 18px}
header{
  height:82px;display:flex;align-items:center;justify-content:space-between;
  border-bottom:1px solid var(--line)
}
.brand{display:flex;gap:12px;align-items:center;letter-spacing:.07em}
.brand-icon{background:var(--navy);color:var(--gold);padding:7px 13px;border-radius:12px;font-size:28px}
.brand strong{font-size:19px;display:block;color:var(--navy)}
.brand em{color:var(--blue);font-style:normal}
.brand small{display:block;color:var(--muted);font-size:10px;letter-spacing:.09em;margin-top:4px}

.intro{
  background:linear-gradient(120deg,#121d3b,#283a74);
  color:#fff;min-height:190px;margin:24px 0;border-radius:24px;
  padding:28px 34px;display:flex;align-items:center;justify-content:space-between;
  overflow:hidden;position:relative
}
.eyebrow{font-size:10px;letter-spacing:.19em;color:#e8c372;font-weight:800}
.intro h1{margin:5px 0;font-size:clamp(28px,4vw,42px);line-height:1.06;letter-spacing:-.04em}
.intro h1 span{color:var(--gold)}
.intro p{color:#cdd5ee;margin:12px 0 0;font-size:15px;max-width:480px}
.intro-knight{font-size:160px;color:#d7e0ff;opacity:.12;position:absolute;right:42px;top:-30px}

.layout{display:grid;grid-template-columns:minmax(0,1fr) 370px;gap:22px;align-items:start}
.board-panel,.card,.login{
  background:var(--panel);border-radius:var(--radius);box-shadow:var(--shadow);
}
.board-panel{padding:18px;min-width:0}
.card{border:1px solid #e6eaf3;padding:20px}
.sidebar{display:flex;flex-direction:column;gap:15px}

.board-top,.board-bottom{
  display:flex;justify-content:space-between;align-items:center;gap:10px
}
.board-top{padding:2px 2px 14px}
.board-bottom{padding:14px 2px 4px}
.player{display:flex;align-items:center;gap:12px;min-width:0}
.player strong{display:block;font-size:15px;line-height:1.2}
.player small{display:block;color:var(--muted);margin-top:4px;font-size:12px;line-height:1.35}
.avatar{
  width:44px;height:44px;display:grid;place-items:center;border-radius:13px;
  font-size:28px;flex:0 0 44px
}
.avatar.dark{background:#1c2742;color:#fff}
.avatar.light{background:#eef2fb;color:#1d2a42}
.tag{font-size:11px;font-weight:800;background:#edf0f7;padding:8px 11px;border-radius:999px;color:#445474;white-space:nowrap}

.board-shell{
  width:min(100%, 680px);
  margin:0 auto;
  border-radius:18px;
  overflow:hidden;
  border:4px solid #7a5538;
  box-shadow:0 2px 0 rgba(122,85,56,.2), 0 8px 18px rgba(70,42,20,.12)
}
.board{
  display:grid;
  grid-template-columns:repeat(8,minmax(0,1fr));
  grid-template-rows:repeat(8,minmax(0,1fr));
  width:100%;
  aspect-ratio:1/1;
  user-select:none;-webkit-user-select:none;touch-action:manipulation;
  overflow:hidden;
}
.square{
  width:100%;height:100%;display:grid;place-items:center;position:relative;
  border:0;border-radius:0;padding:0;margin:0;min-width:0;min-height:0;
  appearance:none;background:transparent;overflow:hidden;
  aspect-ratio:1/1;
}
.square.light{background:var(--light)}
.square.dark{background:var(--dark)}
.square.selected{background:#dcc45a!important}
.square.last{box-shadow:inset 0 0 0 999px rgba(248,226,99,.25)}
.square.target:after{
  content:'';position:absolute;width:24%;height:24%;border-radius:50%;
  background:rgba(45,120,74,.45);pointer-events:none
}
.square.target.occupied:after{
  width:82%;height:82%;border:4px solid rgba(45,120,74,.65);background:transparent
}
.piece{
  font-family:"Apple Symbols","Arial Unicode MS","Segoe UI Symbol","Noto Sans Symbols 2","DejaVu Sans",serif;
  line-height:1;font-size:clamp(27px,5.3vw,54px);z-index:1;pointer-events:none;
  transform:translateY(-1px)
}
.piece.white{color:#fffdf7;text-shadow:0 1px 0 rgba(0,0,0,.5),0 2px 4px rgba(0,0,0,.18)}
.piece.black{color:#273652;text-shadow:0 1px 0 rgba(255,255,255,.45),0 2px 4px rgba(0,0,0,.12)}
.coordinate{position:absolute;font-size:11px;font-weight:800;pointer-events:none;opacity:.92}
.coordinate.rank{left:4px;top:3px}
.coordinate.file{right:4px;bottom:3px}
.light .coordinate{color:#8b6545}
.dark .coordinate{color:#f4e4cf}

.actions{display:flex;gap:10px;margin-top:16px}
.actions button{flex:1;padding:13px 8px;font-size:14px}
.primary,.secondary,.quiet{
  border-radius:13px;padding:12px 14px;font-weight:780;border:1px solid transparent
}
.primary{background:var(--blue);color:white}
.primary:hover{background:#2138bf}
.secondary{background:#eef1fb;color:#283a81}
.secondary:hover{background:#dfe5ff}
.quiet{background:transparent;color:var(--muted)}
.wide{width:100%}

.card-title{display:flex;align-items:center;gap:11px;margin-bottom:18px}
.card-title h2{font-size:15px;margin:0}
.card-title p{margin:4px 0 0;color:var(--muted);font-size:11px}
.round-icon{width:34px;height:34px;border-radius:10px;background:#e7ebff;color:#293cbe;display:grid;place-items:center;font-size:19px;font-weight:bold}
.round-icon.gold{background:#fff4d9;color:#b17d16}
.field{margin-bottom:16px}
.field label{display:flex;justify-content:space-between;font-size:12px;font-weight:800;margin-bottom:8px}
.field select,.login input{width:100%;border:1px solid #dce2ed;border-radius:11px;padding:11px;background:#f8faff;color:var(--ink)}
.field input[type=range]{width:100%;accent-color:var(--blue)}
.subtext{color:var(--muted);font-size:11px;line-height:1.5}
.feedback{background:#f5f7fd;border-left:4px solid var(--blue2);border-radius:8px;padding:14px;color:#2d3a58;font-size:13px;line-height:1.65;margin-bottom:15px;white-space:pre-wrap}
.feedback.good{border-left-color:var(--green);background:#edf9f3}
.feedback.review{border-left-color:#d49b27;background:#fff9ea}
.hintbox,.ai-reply{background:#fff7df;padding:13px;border-radius:10px;font-size:13px;line-height:1.6;margin:12px 0;white-space:pre-wrap}
.ai-reply{background:#eaf0ff}
.lesson-info{margin:0 0 15px}
.progress-track{height:8px;border-radius:99px;background:#e4e9f3;overflow:hidden}
.progress-track>div{width:0;height:100%;background:var(--blue);transition:width .2s}
.lesson-info span{font-size:11px;color:var(--muted)}
.moves{max-height:135px;overflow-y:auto;display:flex;gap:5px;flex-wrap:wrap}
.move{border-radius:7px;background:#f0f3fa;padding:5px 8px;font-size:12px}
.move b{color:var(--muted);font-size:10px;margin-right:5px}
.stats{display:grid;gap:8px}
.stat{display:flex;justify-content:space-between;gap:8px;font-size:12px;border-bottom:1px solid var(--line);padding:7px 0}
.stat strong{color:var(--blue)}
footer{text-align:center;color:var(--muted);padding:25px 0;font-size:11px}

.login{max-width:410px;margin:70px auto;text-align:center;padding:33px}
.login h1{font-size:25px}
.login p{color:var(--muted);font-size:14px}
.login form{display:grid;gap:12px;margin-top:22px}
.hero-icon{font-size:65px;color:var(--blue)}

.modal{position:fixed;inset:0;background:#090e20bd;display:grid;place-items:center;z-index:10;padding:18px}
.modal-card{background:white;border-radius:20px;padding:25px;max-width:350px;width:100%;text-align:center}
.promotion-options{display:flex;justify-content:space-around;margin:20px 0}
.promotion-options button{font-size:41px;border:0;background:#edf0fa;border-radius:12px;padding:8px}
.board-panel.busy{opacity:.78;pointer-events:none}

@media(max-width:900px){
  .layout{grid-template-columns:minmax(0,1fr)}
  .board-panel{max-width:760px;margin:auto;width:100%}
  .sidebar{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));align-items:start}
}

@media(max-width:640px){
  .app{padding:0 10px}
  header{height:68px}
  .brand strong{font-size:16px}
  .brand small{font-size:9px}
  .intro{margin:12px 0;padding:20px;min-height:146px;border-radius:16px}
  .intro p{font-size:13px;max-width:250px}
  .intro-knight{right:-10px;font-size:128px}
  .board-panel{padding:10px;border-radius:14px}
  .board-top{padding:0 1px 12px}
  .board-bottom{padding:12px 1px 2px}
  .board-shell{width:min(calc(100vw - 28px), 680px);border-width:3px;border-radius:14px}
  .player strong{font-size:13px}
  .player small{font-size:11px}
  .avatar{width:40px;height:40px;font-size:25px;border-radius:12px}
  .piece{font-size:clamp(28px,9vw,43px)}
  .coordinate{font-size:10px}
  .actions{gap:6px;flex-wrap:wrap}
  .actions button{min-width:calc(33.333% - 4px);font-size:12px;padding:12px 4px}
  .sidebar{display:flex}
  .card{padding:17px;border-radius:14px}
  .tag{font-size:10px;padding:7px 9px}
}

/* v1.2 – Keep animated pieces inside the board's exact 8 × 8 coordinate system. */
.board{position:relative;isolation:isolate}
.piece-moving{
  position:absolute;display:flex;align-items:center;justify-content:center;
  z-index:30;pointer-events:none;will-change:transform;
  margin:0!important;
  line-height:1;
  box-sizing:border-box;
}
@media(prefers-reduced-motion:reduce){.piece-moving{will-change:auto}}

/* v1.3 — Coach in a compact speech bubble above the board. */
.coach-bubble{
  position:relative;
  margin:0 0 16px;
  border:1px solid #cbd8f3;
  border-radius:17px;
  background:#f4f7ff;
  box-shadow:0 2px 10px rgba(44,71,130,.05);
  overflow:visible;
}
.coach-bubble:after{
  content:"";position:absolute;bottom:-9px;left:29px;
  width:16px;height:16px;background:#f4f7ff;
  transform:rotate(45deg);border-bottom:1px solid #cbd8f3;border-right:1px solid #cbd8f3;
}
.coach-bubble-main{
  display:flex;align-items:flex-start;gap:10px;
  padding:11px 11px 12px;
  position:relative;z-index:1;
}
.coach-avatar{
  width:34px;height:34px;min-width:34px;display:grid;place-items:center;
  border-radius:11px;background:#233b88;color:white;font-size:24px;
}
.coach-message{flex:1;min-width:0}
.coach-heading{display:flex;flex-wrap:wrap;align-items:center;gap:4px 9px;margin-bottom:4px}
.coach-heading strong{font-size:13px;color:#1c315d}
.coach-heading span{font-size:10px;color:#54698f}
.coach-bubble .feedback{
  margin:0;padding:0;border:0;border-radius:0;background:transparent;
  font-size:13px;line-height:1.45;color:#253656;
  display:-webkit-box;-webkit-box-orient:vertical;-webkit-line-clamp:2;line-clamp:2;
  overflow:hidden;white-space:normal;
}
.coach-bubble.expanded .feedback{display:block;overflow:visible;-webkit-line-clamp:unset;line-clamp:unset;white-space:pre-wrap}
.coach-bubble .feedback.good{color:#116448}
.coach-bubble .feedback.review{color:#81540f}
.coach-toggle{
  border:1px solid #d8e0f5;background:#fff;color:#273d7c;
  border-radius:10px;min-width:36px;height:36px;padding:0;
  display:grid;place-items:center;font-size:24px;flex-shrink:0;
}
.coach-bubble.expanded .coach-toggle{transform:none}
.coach-details{
  position:relative;z-index:1;
  padding:0 12px 13px 56px;
  display:flex;flex-direction:column;align-items:stretch;gap:9px;
}
.coach-details .lesson-info{margin:0}
.coach-details .hintbox,.coach-details .ai-reply{margin:0;background:#fff;padding:11px}
.coach-explain{align-self:flex-start;font-size:12px;padding:9px 12px}
@media(max-width:640px){
  .intro{min-height:0;padding:12px 16px;margin:9px 0 11px}
  .intro .eyebrow{font-size:9px}
  .intro h1{font-size:23px;line-height:1.08;margin:4px 0}
  .intro p{display:none}
  .intro-knight{font-size:75px;right:14px;top:-13px}
  .board-top{padding-bottom:10px}
  .coach-bubble{margin-bottom:14px;border-radius:14px}
  .coach-bubble-main{padding:9px;gap:8px}
  .coach-avatar{width:30px;height:30px;min-width:30px;font-size:21px;border-radius:9px}
  .coach-heading strong{font-size:12px}
  .coach-heading span{font-size:9px}
  .coach-bubble .feedback{font-size:12px;line-height:1.36}
  .coach-toggle{min-width:32px;height:32px;font-size:20px}
  .coach-details{padding:0 10px 11px 47px}
}