*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --bg: #eeeeee; --surface: #f9f9f9; --border: #d0d0d0;
  --text: #1a1a1a; --muted: #666; --accent: #2563eb; --accent-hover: #1d4ed8;
  --code-bg: #1e1e2e; --code-text: #cdd6f4;
  --correct-bg: #dcfce7; --correct-text: #166534; --correct-border: #86efac;
  --incorrect-bg: #fee2e2; --incorrect-text: #991b1b; --incorrect-border: #fca5a5;
}
[data-theme="dark"] {
  --bg: #0f0f0f; --surface: #1a1a1a; --border: #2e2e2e;
  --text: #f0f0f0; --muted: #999;
  --correct-bg: #14532d; --correct-text: #86efac; --correct-border: #166534;
  --incorrect-bg: #450a0a; --incorrect-text: #fca5a5; --incorrect-border: #991b1b;
}
body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif; background: var(--bg); color: var(--text); min-height: 100vh; transition: background .25s, color .25s; }

/* ── Nav ── */
nav { display: flex; justify-content: space-between; align-items: center; padding: 14px 24px; background: var(--surface); border-bottom: 1px solid var(--border); }
#brand { font-size: 1.65rem; font-weight: 700; background: none; border: none; color: var(--text); cursor: pointer; text-decoration: none; }
#theme-btn { background: none; border: 1px solid var(--border); border-radius: 6px; padding: 6px 10px; cursor: pointer; font-size: .95rem; color: var(--text); }

.hidden { display: none !important; }

/* ── Layout ── */
main { max-width: 900px; margin: 0 auto; padding: 20px 20px 40px; }

/* ── Home ── */
#page-home { text-align: center; }
#page-home h1 { font-size: 2.8rem; margin-bottom: 8px; line-height: 1.2; text-transform: uppercase; }
#page-home p { font-size: 1.6rem; margin-top: 16px; margin-bottom: 48px; }
.diff-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; }
.diff-btn { padding: 10px 12px; border: 2px solid var(--border); border-radius: 10px; background: var(--surface); color: var(--text); font-size: 1.15rem; font-weight: 600; cursor: pointer; transition: border-color .15s, transform .15s; text-align: center; display: flex; flex-direction: column; align-items: center; text-decoration: none; }
.diff-btn:hover { border-color: var(--accent); transform: translateY(-2px); }
.diff-btn .diff-title { display: block; font-size: 1.15rem; font-weight: 700; margin-bottom: 10px; text-align: center; width: 100%; }
.diff-btn .diff-skills { display: block; font-size: 0.72rem; font-weight: 400; color: var(--muted); line-height: 1.7; text-transform: none; letter-spacing: 0; text-align: center; }

/* ── Learn grid ── */
.section-label { font-size: .75rem; font-weight: 700; text-transform: uppercase; letter-spacing: .1em; color: var(--muted); margin-bottom: 14px; }
.learn-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; margin-bottom: 48px; }
.learn-btn { padding: 18px 12px; border: 2px solid var(--border); border-radius: 10px; background: var(--surface); color: var(--text); font-size: 1.15rem; font-weight: 700; cursor: pointer; transition: border-color .15s, transform .15s; text-align: center; text-decoration: none; display: flex; align-items: center; justify-content: center; }
.learn-btn:hover { border-color: var(--accent); transform: translateY(-2px); }

/* ── Quiz pages ── */
.page-quiz { animation: fadein .25s ease; }
@keyframes fadein { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: translateY(0); } }
.quiz-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: 22px; gap: 16px; }
.badge { font-size: .78rem; font-weight: 600; text-transform: uppercase; letter-spacing: .05em; padding: 4px 12px; border-radius: 20px; border: 1px solid var(--border); color: var(--muted); background: var(--surface); }
.change-diff-btn { font-size: .85rem; padding: 6px 14px; border: 1px solid var(--border); border-radius: 6px; background: var(--surface); color: var(--text); cursor: pointer; transition: border-color .15s, color .15s; text-decoration: none; }
.change-diff-btn:hover { border-color: var(--accent); }
.card { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 18px 20px; }
.card h3 { font-size: .8rem; font-weight: 600; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin-bottom: 10px; }
.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin-bottom: 16px; }
.schema-row { font-size: .95rem; margin-bottom: 6px; color: var(--text); }
.schema-row span { color: var(--muted); }
.task-text { font-size: 1rem; line-height: 1.6; color: var(--text); font-weight: 700; }
.sql-label { display: block; font-size: .85rem; font-weight: 600; margin-bottom: 8px; color: var(--muted); }
.sql-input { width: 100%; padding: 14px; border: 2px solid var(--border); border-radius: 8px; font-family: "Courier New", monospace; font-size: .95rem; resize: vertical; min-height: 120px; background: var(--surface); color: var(--text); transition: border-color .15s; }
.sql-input:focus { outline: none; border-color: var(--accent); }
.sql-input::placeholder { color: var(--muted); opacity: .7; }
.hint { font-size: .78rem; color: var(--muted); margin-top: 6px; }
.btn-row { display: flex; gap: 10px; margin-top: 14px; }
.submit-btn { flex: 1; padding: 14px; background: var(--accent); color: #fff; border: none; border-radius: 8px; font-size: 1rem; font-weight: 600; cursor: pointer; transition: background .15s; }
.submit-btn:hover { background: var(--accent-hover); }
.solution-btn { flex: 1; padding: 14px; background: none; color: var(--muted); border: 1px solid var(--border); border-radius: 8px; font-size: 1rem; font-weight: 600; cursor: pointer; transition: border-color .15s, color .15s; }
.solution-btn:hover { border-color: var(--accent); color: var(--accent); }
.results { margin-top: 20px; animation: fadein .2s ease; }
.verdict { padding: 14px 18px; border-radius: 8px; font-weight: 600; font-size: 1rem; margin-bottom: 16px; border: 1.5px solid; }
.verdict.correct { background: var(--correct-bg); color: var(--correct-text); border-color: var(--correct-border); }
.verdict.incorrect { background: var(--incorrect-bg); color: var(--incorrect-text); border-color: var(--incorrect-border); }
.result-card { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 16px 20px; margin-bottom: 14px; }
.result-card h4 { font-size: .78rem; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin-bottom: 10px; }
.result-card pre { background: var(--code-bg); color: var(--code-text); padding: 14px; border-radius: 6px; overflow-x: auto; font-family: "Courier New", monospace; font-size: .9rem; margin: 0; }
.result-card p { font-size: .95rem; line-height: 1.6; color: var(--text); }
.next-btn { width: 100%; padding: 14px; background: var(--surface); color: var(--text); border: 2px solid var(--accent); border-radius: 8px; font-size: 1rem; font-weight: 600; cursor: pointer; transition: background .15s; }
.next-btn:hover { background: var(--accent); color: #fff; }

/* ── Responsive ── */
@media (max-width: 480px) {
  .diff-grid { grid-template-columns: 1fr; }
  .learn-grid { grid-template-columns: repeat(2, 1fr); }
  .two-col { grid-template-columns: 1fr; }
  #page-home h1 { font-size: 1.8rem; }
}