*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --bg:#0a0a0f;--surface:#13131a;--card:#1c1c26;
  --border:rgba(255,255,255,0.07);--accent:#e8383d;
  --accent-dim:rgba(232,56,61,0.12);--accent-glow:rgba(232,56,61,0.25);
  --text:#f0f0f5;--muted:#6b7280;--muted2:#9ca3af;
  --green:#4ade80;--green-dim:rgba(74,222,128,0.12);
  --sidebar:260px;--font:'Space Grotesk',system-ui,sans-serif;
  --radius:14px;
}
html,body{height:100%;overflow:hidden}
body{font-family:var(--font);background:var(--bg);color:var(--text)}

/* ─── Shared modal base ─── */
.modal-overlay{
  position:fixed;inset:0;
  background:rgba(0,0,0,0.82);backdrop-filter:blur(10px);
  display:flex;align-items:center;justify-content:center;z-index:100
}
.modal-overlay.hidden{display:none}
.modal-card{
  background:var(--surface);border:1px solid var(--border);
  border-radius:20px;padding:48px 40px;width:100%;max-width:420px;
  text-align:center;box-shadow:0 24px 80px rgba(0,0,0,0.5)
}
.modal-badge{
  display:inline-block;padding:4px 12px;background:var(--accent-dim);
  border:1px solid var(--accent-glow);border-radius:20px;
  font-size:11px;font-weight:700;letter-spacing:.1em;
  text-transform:uppercase;color:var(--accent);margin-bottom:24px
}
.modal-card h1{font-size:23px;font-weight:700;margin-bottom:8px;line-height:1.25}
.modal-card h1 span{color:var(--accent)}
.modal-card p{color:var(--muted2);font-size:14px;margin-bottom:28px;line-height:1.5}
.modal-input{
  width:100%;padding:13px 16px;background:var(--card);
  border:1.5px solid var(--border);border-radius:12px;
  color:var(--text);font-family:var(--font);font-size:15px;
  outline:none;transition:border-color .2s;margin-bottom:14px
}
.modal-input:focus{border-color:var(--accent)}
.modal-input::placeholder{color:var(--muted)}
.modal-btn{
  width:100%;padding:13px;background:var(--accent);color:#fff;
  border:none;border-radius:12px;font-family:var(--font);
  font-size:15px;font-weight:600;cursor:pointer;
  transition:opacity .2s,transform .1s;letter-spacing:.01em
}
.modal-btn:hover:not(:disabled){opacity:.88}
.modal-btn:active:not(:disabled){transform:scale(.98)}
.modal-btn:disabled{opacity:.4;cursor:not-allowed}

/* ─── Password screen ─── */
.pass-icon{font-size:36px;margin-bottom:16px;opacity:.6}
.pass-error{
  margin-top:12px;font-size:13px;color:var(--accent);
  min-height:18px;font-weight:500
}

/* ─── App shell ─── */
.app{display:flex;height:100vh}
.app.hidden{display:none}

/* ─── Sidebar ─── */
#sidebar{
  width:var(--sidebar);background:var(--surface);
  border-right:1px solid var(--border);
  display:flex;flex-direction:column;flex-shrink:0
}
.sb-header{padding:22px 20px 18px;border-bottom:1px solid var(--border)}
.sb-bfh{
  font-size:10px;font-weight:700;letter-spacing:.12em;
  text-transform:uppercase;color:var(--muted);margin-bottom:5px
}
.sb-course{font-size:13px;font-weight:600;color:var(--text);line-height:1.35}

.nav-list{list-style:none;padding:12px 10px;flex:1;overflow-y:auto}
.nav-item{margin-bottom:2px}
.nav-btn{
  display:flex;align-items:center;gap:10px;width:100%;
  padding:9px 10px;border-radius:10px;border:none;
  background:transparent;color:var(--muted2);
  font-family:var(--font);font-size:13.5px;font-weight:500;
  cursor:pointer;text-align:left;transition:background .15s,color .15s
}
.nav-btn:hover{background:rgba(255,255,255,0.04);color:var(--text)}
.nav-btn.active{background:var(--accent-dim);color:var(--accent);font-weight:600}
.nav-btn svg{flex-shrink:0;opacity:.7}
.nav-btn.active svg{opacity:1}
.nav-chevron{margin-left:auto;transition:transform .25s}
.nav-chevron.open{transform:rotate(90deg)}

/* Exercises submenu */
.exo-submenu{
  list-style:none;padding:3px 0 3px 32px;
  overflow:hidden;max-height:0;transition:max-height .3s ease
}
.exo-submenu.open{max-height:500px}
.exo-sub-btn{
  display:flex;align-items:center;gap:8px;width:100%;
  padding:7px 10px;border-radius:8px;border:none;
  background:transparent;color:var(--muted2);
  font-family:var(--font);font-size:12.5px;font-weight:500;
  cursor:pointer;text-align:left;transition:background .15s,color .15s
}
.exo-sub-btn:hover:not(.locked){background:rgba(255,255,255,0.04);color:var(--text)}
.exo-sub-btn.active{background:var(--accent-dim);color:var(--accent)}
.exo-sub-btn.locked{opacity:.35;cursor:not-allowed}
.exo-dot{width:5px;height:5px;border-radius:50%;background:currentColor;flex-shrink:0}
.exo-check{margin-left:auto;color:var(--green);font-size:11px}

/* Sidebar download link */
.sb-download{padding:10px 18px;border-top:1px solid var(--border)}
.download-link{
  display:flex;align-items:center;gap:8px;
  padding:8px 10px;border-radius:8px;
  color:var(--muted);font-size:12.5px;font-weight:500;
  text-decoration:none;transition:background .15s,color .15s
}
.download-link:hover{background:rgba(255,255,255,0.04);color:var(--text)}
.download-link svg{flex-shrink:0}

/* Sidebar footer */
.sb-footer{padding:14px 18px 10px;border-top:1px solid var(--border)}
.clear-btn{
  display:block;width:100%;margin-top:10px;padding:0;
  background:none;border:none;text-align:left;
  font-family:var(--font);font-size:11px;color:var(--muted);
  cursor:pointer;transition:color .15s;letter-spacing:.01em
}
.clear-btn:hover{color:var(--accent)}
.student-tag{display:flex;align-items:center;gap:10px}
.student-avatar{
  width:30px;height:30px;border-radius:50%;
  display:flex;align-items:center;justify-content:center;
  font-size:12px;font-weight:700;flex-shrink:0;color:#fff
}
.student-name-sb{font-size:13px;font-weight:600;color:var(--text);white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.student-score-sb{font-size:11px;color:var(--muted);margin-top:1px}

/* ─── Content area ─── */
#content{flex:1;overflow:hidden;position:relative}
.panel{position:absolute;inset:0;display:none;overflow-y:auto;flex-direction:column}
.panel.active{display:flex}

/* Presentation */
#panel-presentation iframe{width:100%;flex:1;border:none}

/* Exercise */
.exo-inner{max-width:700px;margin:0 auto;padding:48px 32px;width:100%}
.exo-eyebrow{
  font-size:10px;font-weight:700;letter-spacing:.12em;
  text-transform:uppercase;color:var(--accent);margin-bottom:10px
}
.exo-h1{font-size:26px;font-weight:700;margin-bottom:6px;line-height:1.2}
.exo-desc{color:var(--muted2);font-size:14px;margin-bottom:28px;line-height:1.5}
.instructions-box{
  background:var(--card);border:1px solid var(--border);
  border-radius:var(--radius);padding:22px 24px;margin-bottom:28px;
  font-size:13.5px;line-height:1.75;color:var(--text);white-space:pre-wrap
}
/* ─── Note box ─── */
.note-box{
  background:rgba(232,56,61,0.06);border:1px solid rgba(232,56,61,0.18);
  border-radius:var(--radius);padding:16px 20px;margin-bottom:24px;
  font-size:13.5px;line-height:1.7;color:var(--text)
}

/* ─── Answer blocks ─── */
.answer-block{margin-bottom:24px}
.answer-label{
  font-size:11px;font-weight:700;letter-spacing:.08em;
  text-transform:uppercase;color:var(--muted);margin-bottom:8px
}
.answer-num{
  display:block;width:160px;padding:12px 16px;
  background:var(--card);border:1.5px solid var(--border);
  border-radius:12px;color:var(--text);font-family:var(--font);
  font-size:24px;font-weight:700;text-align:center;
  outline:none;transition:border-color .2s;
  /* remove browser spin arrows */
  -moz-appearance:textfield
}
.answer-num::-webkit-inner-spin-button,
.answer-num::-webkit-outer-spin-button{-webkit-appearance:none;margin:0}
.answer-num:focus{border-color:var(--accent)}
.answer-num:disabled{opacity:.55;cursor:default}
.answer-ta{
  width:100%;min-height:200px;padding:14px 16px;
  background:var(--card);border:1.5px solid var(--border);
  border-radius:12px;color:var(--text);font-family:var(--font);
  font-size:14px;line-height:1.65;outline:none;resize:vertical;
  transition:border-color .2s;margin-bottom:14px
}
.answer-ta:focus{border-color:var(--accent)}
.answer-ta:disabled{opacity:.55;cursor:default}
.submit-btn{
  padding:11px 26px;background:var(--accent);color:#fff;
  border:none;border-radius:10px;font-family:var(--font);
  font-size:13.5px;font-weight:600;cursor:pointer;
  transition:opacity .2s;letter-spacing:.01em
}
.submit-btn:hover:not(:disabled){opacity:.88}
.submit-btn:disabled{opacity:.4;cursor:not-allowed}
.submitted-banner{
  display:flex;align-items:center;gap:10px;
  padding:12px 18px;background:var(--green-dim);
  border:1px solid rgba(74,222,128,.25);border-radius:10px;
  color:var(--green);font-size:14px;font-weight:600;margin-bottom:20px
}
.score-pill{
  display:inline-flex;align-items:center;
  padding:4px 12px;background:var(--accent-dim);
  border-radius:20px;color:var(--accent);
  font-size:13px;font-weight:700;margin-left:10px
}
.locked-panel{
  display:flex;flex-direction:column;align-items:center;
  justify-content:center;height:100%;gap:14px;color:var(--muted)
}
.lock-icon{font-size:42px;opacity:.25}
.lock-text{font-size:17px;font-weight:600;opacity:.6}
.lock-sub{font-size:13px;opacity:.4}

/* ─── Leaderboard ─── */
.lb-inner{max-width:560px;margin:0 auto;padding:48px 32px;width:100%}
.lb-eyebrow{
  font-size:10px;font-weight:700;letter-spacing:.12em;
  text-transform:uppercase;color:var(--accent);margin-bottom:10px
}
.lb-h1{font-size:26px;font-weight:700;margin-bottom:28px}
.lb-table{
  background:var(--surface);border:1px solid var(--border);
  border-radius:var(--radius);overflow:hidden
}
.lb-row{
  display:flex;align-items:center;gap:14px;
  padding:13px 18px;border-bottom:1px solid var(--border);
  transition:background .15s
}
.lb-row:last-child{border-bottom:none}
.lb-row:hover{background:rgba(255,255,255,0.02)}
.lb-row.me{background:var(--accent-dim)}
.lb-rank{font-size:13px;font-weight:700;color:var(--muted);width:22px;text-align:center;flex-shrink:0}
.lb-medal{font-size:16px;width:22px;text-align:center;flex-shrink:0}
.lb-avatar{
  width:34px;height:34px;border-radius:50%;
  display:flex;align-items:center;justify-content:center;
  font-size:13px;font-weight:700;color:#fff;flex-shrink:0
}
.lb-name{flex:1;font-size:14px;font-weight:500}
.lb-name .you{
  font-size:10px;font-weight:700;letter-spacing:.08em;
  text-transform:uppercase;color:var(--accent);margin-left:8px;opacity:.8
}
.lb-pts{font-size:16px;font-weight:700;color:var(--accent)}
.lb-pts small{font-size:11px;color:var(--muted);font-weight:400;margin-left:2px}
.lb-empty{text-align:center;padding:48px;color:var(--muted);font-size:14px}

/* ─── Toast ─── */
.toast{
  position:fixed;bottom:24px;right:24px;
  padding:12px 18px;background:var(--card);border:1px solid var(--border);
  border-radius:12px;font-size:13.5px;font-weight:500;
  box-shadow:0 8px 32px rgba(0,0,0,0.4);z-index:200;
  opacity:0;transform:translateY(6px);
  transition:opacity .25s,transform .25s;pointer-events:none
}
.toast.show{opacity:1;transform:translateY(0)}
.toast.ok{border-color:rgba(74,222,128,.4);color:var(--green)}
.toast.err{border-color:var(--accent-glow);color:var(--accent)}