*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --black: #050505;
  --panel: #0a0a0d;
  --panel2: #101014;
  --white: #f5f2f7;
  --muted: #aaa4af;
  --purple: #b44fff;
  --purple2: #7c1bb7;
  --green: #66ff99;
  --red: #ff5d68;
  --line: #29252e;
}

html { background: var(--black); }
body {
  min-height: 100vh;
  background:
    radial-gradient(circle at 72% 15%, rgba(128, 31, 190, .12), transparent 28%),
    var(--black);
  color: var(--white);
  font-family: Arial, Helvetica, sans-serif;
}

code, pre, textarea { font-family: Consolas, "Courier New", monospace; }

.course-bar {
  min-height: 64px;
  position: sticky;
  top: 0;
  z-index: 30;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  padding: 0 28px;
  background: rgba(0,0,0,.96);
  border-bottom: 1px solid rgba(180,79,255,.38);
}

.brand {
  color: #fff;
  text-decoration: none;
  font-family: Georgia, "Times New Roman", serif;
  font-weight: 700;
  letter-spacing: .16em;
  font-size: .83rem;
}

.course-title {
  color: var(--muted);
  font-size: .66rem;
  font-weight: 800;
  letter-spacing: .22em;
}

.codex-btn {
  justify-self: end;
  color: var(--purple);
  background: transparent;
  border: 1px solid rgba(180,79,255,.55);
  padding: 9px 14px;
  cursor: pointer;
  font-size: .66rem;
  font-weight: 900;
  letter-spacing: .18em;
}

.course-shell {
  min-height: calc(100vh - 64px);
  display: grid;
  grid-template-columns: 270px minmax(0, 1fr);
}

.progress-panel {
  padding: 34px 22px;
  background: #08080a;
  border-right: 1px solid var(--line);
}

.progress-kicker, .lesson-tag, .block-label {
  color: var(--purple);
  font-size: .65rem;
  font-weight: 900;
  letter-spacing: .2em;
}

.progress-number {
  margin: 12px 0;
  font-family: Georgia, "Times New Roman", serif;
  font-size: 3rem;
  font-weight: 700;
}

.progress-number span {
  color: #58535d;
  font-size: 1rem;
}

.progress-track {
  height: 3px;
  background: #262229;
}

.progress-fill {
  width: 10%;
  height: 100%;
  background: var(--purple);
  box-shadow: 0 0 10px rgba(180,79,255,.8);
}

.progress-panel > p {
  margin: 10px 0 26px;
  color: #6f6973;
  font-size: .72rem;
}

.lesson-list {
  display: grid;
  gap: 4px;
}

.lesson {
  width: 100%;
  min-height: 48px;
  display: grid;
  grid-template-columns: 32px 1fr;
  gap: 7px;
  align-items: center;
  border: 0;
  border-left: 2px solid transparent;
  padding: 9px 10px;
  text-align: left;
  color: #77717b;
  background: transparent;
  font-size: .74rem;
}

.lesson span { line-height: 1.25; }

.lesson.active {
  color: white;
  border-left-color: var(--purple);
  background: rgba(180,79,255,.08);
}

.lesson.locked::after {
  content: "•";
  color: #3f3b42;
}

.lesson-panel {
  width: min(880px, 100%);
  padding: clamp(42px, 7vw, 90px) clamp(24px, 7vw, 86px) 100px;
  margin: 0 auto;
}

.lesson-top {
  padding-bottom: 38px;
  border-bottom: 1px solid var(--line);
}

.lesson-top h1 {
  margin-top: 14px;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(2.7rem, 6vw, 5.3rem);
  line-height: .92;
  letter-spacing: -.035em;
}

.lesson-top h1 span { color: var(--purple); }

.lesson-intro {
  margin-top: 20px;
  color: #c9c4cc;
  font-size: 1.05rem;
}

.lesson-block {
  padding: 30px 0;
  border-bottom: 1px solid #1c1a1f;
}

.lesson-block > p {
  margin-top: 12px;
  color: #d2cdd5;
  line-height: 1.75;
}

.lesson-block code, .task-copy code {
  color: var(--green);
}

.know-grid {
  margin-top: 15px;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
}

.know-grid div {
  min-height: 90px;
  padding: 18px;
  background: var(--panel2);
  border: 1px solid #25222a;
}

.know-grid b {
  display: block;
  margin-bottom: 8px;
  color: var(--green);
  font-family: Consolas, monospace;
  font-size: 1.15rem;
}

.know-grid span {
  color: var(--muted);
  font-size: .76rem;
}

.example-block pre {
  margin-top: 16px;
  padding: 22px;
  overflow-x: auto;
  background: #080a09;
  border-left: 3px solid var(--green);
  color: var(--green);
  font-size: 1rem;
}

.example-note {
  color: #7f7883 !important;
  font-size: .78rem;
}

.challenge {
  margin-top: 42px;
  padding: clamp(22px, 4vw, 34px);
  border: 1px solid rgba(180,79,255,.48);
  background: linear-gradient(145deg, rgba(16,13,20,.98), rgba(5,5,7,.98));
}

.challenge-head {
  display: flex;
  gap: 20px;
  justify-content: space-between;
  align-items: flex-start;
}

.challenge h2 {
  margin-top: 8px;
  font-family: Georgia, "Times New Roman", serif;
  font-size: clamp(1.4rem, 3vw, 2.2rem);
}

.python-status {
  display: flex;
  align-items: center;
  gap: 7px;
  white-space: nowrap;
  color: #88828c;
  font-size: .58rem;
  font-weight: 900;
  letter-spacing: .12em;
}

.python-status span {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: #d69cff;
  box-shadow: 0 0 9px rgba(180,79,255,.9);
}

.python-status.ready { color: var(--green); }
.python-status.ready span {
  background: var(--green);
  box-shadow: 0 0 9px rgba(102,255,153,.8);
}

.task-copy {
  margin: 19px 0 22px;
  color: #c8c2cb;
  line-height: 1.6;
  font-size: .92rem;
}

.editor-label {
  display: block;
  margin-bottom: 8px;
  color: #716b75;
  font-size: .59rem;
  font-weight: 900;
  letter-spacing: .18em;
}

.editor-wrap {
  min-height: 180px;
  display: grid;
  grid-template-columns: 42px 1fr;
  background: #020303;
  border: 1px solid #2b2830;
}

.line-num {
  padding-top: 17px;
  text-align: center;
  color: #55505a;
  border-right: 1px solid #1c1b1e;
  font-family: Consolas, monospace;
  font-size: .85rem;
}

#codeEditor {
  width: 100%;
  min-height: 180px;
  resize: vertical;
  border: 0;
  outline: 0;
  padding: 16px;
  background: transparent;
  color: #eae6ed;
  font-size: 16px;
  line-height: 1.6;
  caret-color: var(--purple);
}

#codeEditor::placeholder { color: #48434c; }

.actions {
  margin-top: 14px;
  display: flex;
  gap: 10px;
}

.run-btn, .reset-btn {
  min-height: 48px;
  border: 1px solid var(--purple);
  padding: 0 22px;
  color: white;
  font-weight: 900;
  letter-spacing: .1em;
  cursor: pointer;
}

.run-btn {
  flex: 1;
  background: var(--purple2);
}

.run-btn:disabled {
  cursor: wait;
  opacity: .45;
}

.reset-btn {
  background: transparent;
}

.terminal {
  margin-top: 22px;
  background: #010302;
  border: 1px solid #202521;
}

.terminal-head {
  min-height: 34px;
  padding: 0 12px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  color: #726f73;
  border-bottom: 1px solid #1c201d;
  font-size: .56rem;
  font-weight: 900;
  letter-spacing: .15em;
}

#output {
  min-height: 90px;
  padding: 17px;
  overflow-x: auto;
  white-space: pre-wrap;
  color: var(--green);
  font-size: .9rem;
  line-height: 1.55;
}

.feedback {
  display: none;
  margin-top: 15px;
  padding: 14px 16px;
  border: 1px solid;
  line-height: 1.45;
  font-size: .86rem;
}

.feedback.good {
  display: block;
  color: var(--green);
  border-color: rgba(102,255,153,.42);
  background: rgba(102,255,153,.05);
}

.feedback.bad {
  display: block;
  color: #ff9ca3;
  border-color: rgba(255,93,104,.42);
  background: rgba(255,93,104,.05);
}

.codex-drawer {
  display: none;
  position: fixed;
  inset: 0;
  z-index: 100;
  padding: 18px;
  align-items: center;
  justify-content: center;
  background: rgba(0,0,0,.82);
  backdrop-filter: blur(8px);
}

.codex-drawer.open { display: flex; }

.codex-card {
  width: min(620px, 100%);
  max-height: 88vh;
  overflow-y: auto;
  position: relative;
  padding: clamp(25px, 5vw, 46px);
  background: #0b0b0e;
  border: 1px solid rgba(180,79,255,.55);
}

.codex-card h2 {
  margin: 8px 0 25px;
  color: var(--purple);
  font-family: Consolas, monospace;
  font-size: 2.5rem;
}

.codex-card h3 {
  margin: 22px 0 8px;
  color: #77717b;
  font-size: .65rem;
  letter-spacing: .15em;
}

.codex-card p { line-height: 1.65; color: #d0cad3; }
.codex-card pre {
  padding: 15px;
  background: #020302;
  color: var(--green);
}

.codex-close {
  position: absolute;
  top: 12px;
  right: 16px;
  color: white;
  background: none;
  border: 0;
  font-size: 2rem;
  cursor: pointer;
}

@media (max-width: 780px) {
  .course-bar {
    grid-template-columns: 1fr auto;
    padding: 0 14px;
  }

  .course-title { display: none; }

  .course-shell { display: block; }

  .progress-panel {
    padding: 15px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .progress-number, .lesson-list { display: none; }

  .progress-panel > p {
    margin: 8px 0 0;
  }

  .lesson-panel {
    padding: 38px 16px 70px;
  }

  .lesson-top h1 { font-size: clamp(3rem, 16vw, 4.5rem); }

  .know-grid { grid-template-columns: 1fr; }

  .challenge { padding: 20px 14px; }

  .challenge-head {
    display: block;
  }

  .python-status {
    margin-top: 13px;
  }

  .editor-wrap {
    min-height: 160px;
    grid-template-columns: 32px 1fr;
  }

  #codeEditor {
    min-height: 160px;
    font-size: 16px;
    padding: 13px 10px;
  }

  .actions {
    display: grid;
    grid-template-columns: 1fr;
  }

  .run-btn, .reset-btn { width: 100%; }

  .brand {
    font-size: .67rem;
    letter-spacing: .1em;
  }
}

@media (max-width: 380px) {
  .codex-btn { padding: 8px 9px; }
  .lesson-top h1 { font-size: 2.8rem; }
}