:root {
  --bg: #f5f7fb;
  --panel: #ffffff;
  --ink: #172033;
  --muted: #637083;
  --line: #d9e1ec;
  --blue: #2563eb;
  --blue-dark: #1d4ed8;
  --green: #16825d;
  --red: #c0392b;
  --amber: #9a6700;
  --code: #111827;
  --shadow: 0 12px 34px rgba(23, 32, 51, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: "Microsoft YaHei", "Segoe UI", Arial, sans-serif;
  line-height: 1.55;
}

button,
input,
select,
textarea {
  font: inherit;
}

button {
  min-height: 40px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 0 14px;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
}

button:hover {
  border-color: #9db2d4;
}

button.primary {
  border-color: var(--blue);
  background: var(--blue);
  color: #fff;
}

button.primary:hover {
  background: var(--blue-dark);
}

button.ghost {
  background: transparent;
}

input,
select,
textarea {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 10px 12px;
  background: #fff;
  color: var(--ink);
}

textarea {
  min-height: 92px;
  resize: vertical;
}

label {
  display: grid;
  gap: 6px;
  color: #344057;
  font-size: 14px;
}

.app-shell {
  min-height: 100vh;
}

.auth-screen {
  min-height: 100vh;
  display: grid;
  place-items: center;
  padding: 28px;
}

.auth-panel {
  width: min(920px, 100%);
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 28px;
  align-items: center;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
  padding: 36px;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--blue);
  font-weight: 700;
}

h1,
h2,
h3 {
  margin: 0;
  line-height: 1.22;
}

h1 {
  font-size: 36px;
}

h2 {
  font-size: 24px;
}

h3 {
  font-size: 18px;
}

.muted {
  color: var(--muted);
}

.stack {
  display: grid;
  gap: 14px;
}

.button-row {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.message {
  min-height: 24px;
  margin: 0;
  color: var(--red);
}

.layout {
  display: grid;
  grid-template-columns: 240px 1fr;
  min-height: 100vh;
}

.sidebar {
  background: #111827;
  color: #f8fafc;
  padding: 22px 16px;
  display: flex;
  flex-direction: column;
  gap: 18px;
}

.brand {
  padding: 0 8px 14px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.14);
}

.brand strong {
  display: block;
  font-size: 20px;
}

.brand span {
  color: #aab5c5;
  font-size: 13px;
}

.nav {
  display: grid;
  gap: 8px;
}

.nav button {
  width: 100%;
  justify-content: flex-start;
  text-align: left;
  background: transparent;
  color: #dbe5f5;
  border-color: transparent;
}

.nav button.active,
.nav button:hover {
  background: rgba(255, 255, 255, 0.1);
  border-color: rgba(255, 255, 255, 0.14);
}

.content {
  padding: 28px;
  display: grid;
  gap: 18px;
  align-content: start;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 18px;
  box-shadow: var(--shadow);
}

.metric {
  display: grid;
  gap: 6px;
}

.metric strong {
  font-size: 28px;
}

.lesson-steps {
  display: grid;
  gap: 14px;
}

.step {
  border-left: 4px solid var(--blue);
}

.code-block {
  overflow: auto;
  max-height: 440px;
  padding: 16px;
  border-radius: 8px;
  background: var(--code);
  color: #edf2ff;
  font-family: Consolas, "Courier New", monospace;
  font-size: 14px;
  white-space: pre;
}

.hidden {
  display: none;
}

.code-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.hint-panel,
.practice-box,
.second-practice {
  display: grid;
  gap: 8px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #f8fafc;
}

.second-practice {
  margin-top: 6px;
  border-color: #bfdbfe;
  background: #eff6ff;
}

.list {
  display: grid;
  gap: 10px;
}

.item {
  display: grid;
  gap: 8px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.status {
  display: inline-flex;
  width: fit-content;
  border-radius: 999px;
  padding: 3px 10px;
  background: #eef2ff;
  color: #3142a0;
  font-size: 13px;
}

.status.good {
  background: #e7f7ef;
  color: var(--green);
}

.status.warn {
  background: #fff7df;
  color: var(--amber);
}

.form-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.full {
  grid-column: 1 / -1;
}

.danger {
  color: var(--red);
}

@media (max-width: 820px) {
  .auth-panel,
  .layout,
  .grid,
  .form-grid {
    grid-template-columns: 1fr;
  }

  .sidebar {
    min-height: auto;
  }

  h1 {
    font-size: 30px;
  }
}