:root {
  --bg: #0d1117;
  --panel: #161b22;
  --panel-2: #1c2230;
  --border: #2a3038;
  --text: #e6edf3;
  --muted: #8b949e;
  --accent: #2f81f7;
  --accent-2: #1f6feb;
  --green: #3fb950;
  --yellow: #d29922;
  --red: #f85149;
  --mono: ui-monospace, "JetBrains Mono", "SF Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }
html, body { height: 100%; margin: 0; }
body {
  background: var(--bg);
  color: var(--text);
  font: 14px/1.55 system-ui, -apple-system, Segoe UI, Roboto, sans-serif;
  display: flex;
  flex-direction: column;
  overflow: hidden;
}
button, select, input, textarea { font-family: inherit; }
a { color: inherit; text-decoration: none; }
.hidden { display: none !important; }

/* ---------- Top bar ---------- */
.topbar {
  flex: 0 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 18px;
  background: var(--panel);
  border-bottom: 1px solid var(--border);
}
.brand { display: flex; align-items: center; gap: 9px; font-weight: 700; font-size: 18px; }
.logo { color: var(--accent); font-family: var(--mono); }
.mainnav { display: flex; gap: 4px; margin-left: 18px; flex: 1; }
.navlink { padding: 7px 14px; border-radius: 7px; color: var(--muted); font-weight: 600; font-size: 14px; }
.navlink:hover { color: var(--text); background: var(--panel-2); }
.navlink.active { color: #fff; background: var(--accent-2); }
.topbar-right { display: flex; align-items: center; gap: 12px; }
.user-box { display: flex; align-items: center; gap: 8px; }
.link { color: var(--accent); }
.link:hover { text-decoration: underline; }
.progress { display: flex; align-items: center; gap: 10px; }
.progress-bar { width: 90px; height: 7px; background: var(--panel-2); border-radius: 999px; overflow: hidden; border: 1px solid var(--border); }
#progress-fill { height: 100%; width: 0%; background: var(--green); transition: width .4s ease; }
.pill {
  background: var(--panel-2);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 12px;
  color: var(--muted);
  white-space: nowrap;
}

/* ---------- Badges ---------- */
.badge { font-size: 12px; padding: 3px 11px; border-radius: 999px; font-weight: 600; white-space: nowrap; }
.badge.Easy { color: var(--green); background: rgba(63,185,80,.14); }
.badge.Medium { color: var(--yellow); background: rgba(210,153,34,.14); }
.badge.Hard { color: var(--red); background: rgba(248,81,73,.14); }

/* =================================================== */
/* LIST VIEW                                            */
/* =================================================== */
.view-list { flex: 1; overflow-y: auto; padding: 0 0 60px; }
.hero { max-width: 860px; margin: 0 auto; padding: 40px 24px 18px; }
.hero h1 { font-size: 30px; margin: 0 0 10px; letter-spacing: -.5px; }
.hero p { color: var(--muted); font-size: 15px; margin: 0; }
.hero b { color: var(--text); }

.list-controls {
  max-width: 860px;
  margin: 0 auto;
  padding: 8px 24px 16px;
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  align-items: center;
}
#search {
  flex: 1;
  min-width: 200px;
  padding: 10px 14px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font-size: 15px;
}
#search:focus { outline: none; border-color: var(--accent); }
.filters { display: flex; gap: 6px; }
.chip {
  background: var(--panel);
  border: 1px solid var(--border);
  color: var(--muted);
  border-radius: 8px;
  padding: 9px 16px;
  font-size: 13px;
  cursor: pointer;
  transition: .12s;
}
.chip:hover { color: var(--text); }
.chip.active { color: #fff; border-color: var(--accent); background: var(--accent-2); }

.table-wrap { max-width: 860px; margin: 0 auto; padding: 0 24px; }
.problem-table { width: 100%; border-collapse: collapse; }
.problem-table thead th {
  text-align: left;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: .5px;
  color: var(--muted);
  padding: 8px 12px;
  border-bottom: 1px solid var(--border);
  font-weight: 600;
}
.problem-table tbody tr {
  cursor: pointer;
  border-bottom: 1px solid var(--border);
  transition: background .1s;
}
.problem-table tbody tr:hover { background: var(--panel); }
.problem-table td { padding: 14px 12px; vertical-align: middle; }
.c-status { width: 28px; }
.c-num { width: 40px; color: var(--muted); }
.c-diff { width: 120px; }
.c-tags { width: 200px; }
.row-title { font-weight: 600; font-size: 15px; }
.row-check { color: var(--green); font-size: 15px; }
.row-tags { color: var(--muted); font-size: 12px; }
.empty { text-align: center; color: var(--muted); padding: 40px; }

/* =================================================== */
/* SOLVE VIEW                                           */
/* =================================================== */
.view-solve { flex: 1; display: flex; flex-direction: column; min-height: 0; }
.solve-header {
  flex: 0 0 auto;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 8px 14px;
  background: var(--panel);
  border-bottom: 1px solid var(--border);
}
.solve-title { font-weight: 700; font-size: 15px; max-width: 38vw; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.spacer { flex: 1; }
.iconbtn {
  background: var(--panel-2);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 7px;
  padding: 7px 12px;
  font-size: 13px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
}
.iconbtn:hover { border-color: var(--accent); }
.iconbtn:disabled { opacity: .4; cursor: not-allowed; }
#language {
  background: var(--panel-2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 7px;
  padding: 7px 10px;
  font-size: 14px;
}

.split { flex: 1; display: grid; grid-template-columns: 1fr 1fr; min-height: 0; }

/* Description pane */
.desc-pane { overflow-y: auto; padding: 22px 26px; border-right: 1px solid var(--border); }
.meta { display: flex; align-items: center; gap: 12px; margin-bottom: 14px; }
.tags { color: var(--muted); font-size: 12px; }
.solved-tag { color: var(--green); font-size: 12px; font-weight: 600; }
.desc { font-size: 15px; line-height: 1.7; }
.desc code, .example code, .hint-box code { font-family: var(--mono); background: var(--panel-2); padding: 1px 6px; border-radius: 4px; font-size: 13px; }
.example {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 9px;
  padding: 12px 16px;
  margin: 14px 0;
}
.example h4 { margin: 0 0 8px; font-size: 12px; color: var(--muted); text-transform: uppercase; letter-spacing: .5px; }
.example pre { margin: 6px 0; font-family: var(--mono); font-size: 13px; white-space: pre-wrap; }
.hint-box {
  margin-top: 20px;
  padding: 12px 16px;
  border-left: 3px solid var(--accent);
  background: var(--panel);
  border-radius: 0 8px 8px 0;
  font-size: 13px;
  color: var(--muted);
}
.hint-box b { color: var(--text); }

/* Editor pane */
.editor-pane { display: flex; flex-direction: column; min-height: 0; }
.editor-toolbar {
  flex: 0 0 auto;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-bottom: 1px solid var(--border);
  background: var(--panel);
}
.btn {
  background: var(--panel-2);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 7px;
  padding: 8px 16px;
  font-size: 14px;
  cursor: pointer;
  transition: .12s;
}
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--green); border-color: var(--green); color: #07210d; font-weight: 700; }
.btn.primary:hover { filter: brightness(1.08); }
.btn.ghost { background: transparent; color: var(--muted); }
.btn:disabled { opacity: .55; cursor: progress; }
#editor { flex: 1; min-height: 0; }

/* Console */
.console { flex: 0 0 38%; min-height: 150px; border-top: 1px solid var(--border); display: flex; flex-direction: column; background: var(--panel); }
.console-tabs { flex: 0 0 auto; display: flex; border-bottom: 1px solid var(--border); }
.ctab { background: none; border: none; color: var(--muted); padding: 9px 16px; cursor: pointer; font-size: 13px; border-bottom: 2px solid transparent; }
.ctab.active { color: var(--text); border-bottom-color: var(--accent); }
.console-body { flex: 1; overflow: auto; min-height: 0; }
#output { margin: 0; padding: 13px 16px; font-family: var(--mono); font-size: 13px; white-space: pre-wrap; line-height: 1.5; }
#custom-input { width: 100%; height: 100%; border: none; background: var(--bg); color: var(--text); font-family: var(--mono); font-size: 14px; padding: 13px 16px; resize: none; }
#custom-input:focus { outline: none; }
.ok { color: var(--green); }
.fail { color: var(--red); }
.dim { color: var(--muted); }

/* Mobile solve tab bar (hidden on desktop) */
.solve-tabs { display: none; }

/* Toast */
.toast {
  position: fixed;
  bottom: 26px;
  left: 50%;
  transform: translateX(-50%) translateY(20px);
  background: var(--green);
  color: #07210d;
  font-weight: 700;
  padding: 12px 24px;
  border-radius: 10px;
  box-shadow: 0 8px 30px rgba(0,0,0,.4);
  opacity: 0;
  transition: .3s;
  z-index: 100;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }

/* =================================================== */
/* RESPONSIVE / MOBILE                                 */
/* =================================================== */
@media (max-width: 820px) {
  .hero { padding: 26px 18px 12px; }
  .hero h1 { font-size: 23px; }
  .hero p { font-size: 14px; }
  .list-controls { padding: 8px 16px 14px; }
  .table-wrap { padding: 0 8px; }
  .problem-table td, .problem-table th { padding: 13px 8px; }
  .c-num, .c-tags { display: none; }
  .row-title { font-size: 15px; }

  /* Solve view: one pane at a time via body[data-pane] */
  .solve-header { flex-wrap: wrap; padding: 8px 10px; gap: 8px; }
  .solve-title { max-width: 50vw; }
  #prev-btn, #next-btn { padding: 7px 9px; }
  #language { margin-left: auto; }

  .split { grid-template-columns: 1fr; padding-bottom: 54px; }
  .desc-pane, .editor-pane { display: none; border-right: none; }
  body[data-pane="desc"] .desc-pane { display: block; }
  body[data-pane="editor"] .editor-pane { display: flex; }
  .editor-pane { height: calc(100% ); }

  .solve-tabs {
    display: flex;
    position: fixed;
    bottom: 0; left: 0; right: 0;
    height: 54px;
    background: var(--panel);
    border-top: 1px solid var(--border);
    z-index: 50;
  }
  .stab {
    flex: 1;
    background: none;
    border: none;
    color: var(--muted);
    font-size: 14px;
    cursor: pointer;
    border-top: 2px solid transparent;
  }
  .stab.active { color: var(--accent); border-top-color: var(--accent); }

  /* avoid iOS zoom on focus */
  #search, #language, .btn, #custom-input, .iconbtn, #auth-user, #auth-pass, .lesson-code { font-size: 16px; }
}

/* =================================================== */
/* LEARN — language grid                               */
/* =================================================== */
.view-learn { flex: 1; overflow-y: auto; padding: 0 0 60px; }
.lang-grid {
  max-width: 980px;
  margin: 0 auto;
  padding: 8px 24px;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(210px, 1fr));
  gap: 14px;
}
.lang-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px;
  cursor: pointer;
  transition: .14s;
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.lang-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.lang-card .lc-top { display: flex; align-items: center; justify-content: space-between; }
.lang-card .lc-name { font-size: 17px; font-weight: 700; }
.lang-card .lc-icon { font-family: var(--mono); color: var(--accent); font-size: 15px; }
.lang-card .lc-meta { color: var(--muted); font-size: 12px; }
.lc-bar { height: 6px; background: var(--panel-2); border-radius: 999px; overflow: hidden; }
.lc-bar > div { height: 100%; background: var(--green); width: 0%; transition: width .3s; }
.lc-done { color: var(--green); font-weight: 600; }

/* =================================================== */
/* COURSE — lessons                                    */
/* =================================================== */
.view-course { flex: 1; display: flex; flex-direction: column; min-height: 0; }
.lesson-list { width: 280px; border-right: 1px solid var(--border); overflow-y: auto; background: var(--panel); padding: 8px 0; }
.split:has(.lesson-list) { grid-template-columns: 280px 1fr; }
.lesson-item {
  display: flex; align-items: center; gap: 10px;
  padding: 13px 18px; cursor: pointer; border-bottom: 1px solid var(--border);
}
.lesson-item:hover { background: var(--panel-2); }
.lesson-item.active { background: var(--panel-2); border-left: 3px solid var(--accent); }
.lesson-item .li-check { width: 18px; color: var(--green); }
.lesson-item .li-title { flex: 1; font-size: 14px; }
.lesson-item .li-num { color: var(--muted); font-size: 12px; }

.lesson-pane { overflow-y: auto; padding: 24px 30px; max-width: 760px; }
.lesson-step { color: var(--accent); font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .6px; }
#lesson-title { font-size: 24px; margin: 6px 0 14px; }
.lesson-editor-wrap { border: 1px solid var(--border); border-radius: 10px; overflow: hidden; margin: 18px 0; }
.lesson-toolbar { display: flex; align-items: center; gap: 8px; padding: 8px 12px; background: var(--panel); border-bottom: 1px solid var(--border); font-size: 12px; }
.lesson-code {
  width: 100%; min-height: 150px; resize: vertical; border: none;
  background: #0a0e14; color: var(--text); font-family: var(--mono); font-size: 13.5px;
  padding: 14px; line-height: 1.55; display: block;
}
.lesson-code:focus { outline: none; }
.lesson-output { margin: 0; padding: 12px 14px; background: var(--panel); border-top: 1px solid var(--border); font-family: var(--mono); font-size: 13px; white-space: pre-wrap; max-height: 220px; overflow: auto; }
.lesson-nav { display: flex; gap: 10px; align-items: center; margin-top: 8px; flex-wrap: wrap; }
.lesson-nav .btn.primary.done { background: var(--panel-2); border-color: var(--green); color: var(--green); }

/* =================================================== */
/* AUTH MODAL                                          */
/* =================================================== */
.overlay {
  position: fixed; inset: 0; z-index: 200;
  background: rgba(2,5,10,.7);
  display: flex; align-items: center; justify-content: center;
  padding: 20px;
}
.modal {
  position: relative;
  width: 100%; max-width: 380px;
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 28px 26px;
}
.modal h2 { margin: 0 0 6px; font-size: 22px; }
.modal-close { position: absolute; top: 14px; right: 16px; background: none; border: none; color: var(--muted); font-size: 18px; cursor: pointer; }
#auth-form { display: flex; flex-direction: column; gap: 10px; margin-top: 18px; }
#auth-user, #auth-pass {
  padding: 11px 14px; background: var(--panel-2); border: 1px solid var(--border);
  border-radius: 8px; color: var(--text); font-size: 15px;
}
#auth-user:focus, #auth-pass:focus { outline: none; border-color: var(--accent); }
.btn.wide { width: 100%; padding: 12px; margin-top: 4px; }
.auth-error { color: var(--red); font-size: 13px; margin: 2px 0 0; }
.auth-toggle { text-align: center; color: var(--muted); font-size: 13px; margin: 16px 0 0; }
.auth-toggle a { color: var(--accent); }

@media (max-width: 820px) {
  .mainnav { margin-left: 6px; gap: 0; }
  .navlink { padding: 6px 10px; font-size: 13px; }
  .progress { display: none; }
  .lang-grid { grid-template-columns: 1fr 1fr; gap: 10px; padding: 8px 14px; }
  .lesson-list { display: none; width: 100%; }
  body[data-cpane="list"] .lesson-list { display: block; }
  body[data-cpane="lesson"] .lesson-pane { display: block; }
  body[data-cpane="list"] .lesson-pane { display: none; }
  .split:has(.lesson-list) { grid-template-columns: 1fr; padding-bottom: 54px; }
  .view-course .split { padding-bottom: 54px; }
}