/* ==========================================================================
   Hóa 10 — Chương 4: Phản ứng oxi hóa – khử — CSS riêng cho chương này.
   Không sửa tool-common.css (dùng chung cho mọi chương) — theo đúng quy
   ước trong QUY_TRINH_THEM_CHUONG_MOI.md.

   Thêm cặp màu đỏ (nhường electron / chất khử / SOH tăng) và xanh dương
   (nhận electron / chất oxi hóa / SOH giảm), và token --teal/--teal-dark
   (accent riêng của chương, không đụng --blue của tool-common.css).
   ========================================================================== */

:root {
  --teal: #0f6e56;
  --teal-dark: #085041;
  --give: #c4342f;        /* chất khử — nhường e — SOH tăng */
  --give-bg: #fdeeed;
  --give-line: #f0c4c1;
  --take: #275fc4;        /* chất oxi hóa — nhận e — SOH giảm */
  --take-bg: #eaf0fd;
  --take-line: #c3d3f5;
}

/* --- Vài class dùng chung với công cụ nhập liệu (không có sẵn trong
   tool-common.css, port từ style.css gốc của app chemistry-builder) --- */
.input-row { display: flex; gap: 10px; }
.btn-primary {
  background: var(--teal); color: #fff; border: none;
  padding: 12px 22px; border-radius: var(--radius, 10px);
  font-size: 15px; font-weight: 600; cursor: pointer;
  transition: background 0.15s; white-space: nowrap; font-family: inherit;
}
.btn-primary:hover { background: var(--teal-dark); }
.btn-secondary {
  background: #fff; color: var(--teal-dark); border: 1px solid var(--teal);
  border-radius: 8px; cursor: pointer; transition: all 0.2s;
  padding: 8px 14px; font-size: 13px; font-weight: 600; font-family: inherit;
}
.btn-secondary:hover { background: #e2f0ec; }
.balanced-eq {
  font-family: "IBM Plex Mono", "SF Mono", Menlo, monospace;
  font-size: 19px; font-weight: 700; color: var(--teal-dark); margin-bottom: 16px;
}
.check-table { width: 100%; border-collapse: collapse; font-size: 14px; }
.check-table th, .check-table td { text-align: left; padding: 6px 10px; border-bottom: 1px solid var(--line); }
.check-table td.ok { color: var(--teal); }
.check-table td.bad { color: var(--error); }

#tab-chapter4.panel.active { display: block; }

.l4 {
  max-width: 980px;
  margin: 0 auto;
}

/* --- Stepper điều hướng 4 giai đoạn --- */
.l4-stepper {
  position: sticky;
  top: 0;
  z-index: 5;
  display: flex;
  gap: 6px;
  padding: 10px 0 18px;
  background: var(--paper);
  overflow-x: auto;
}
.l4-step-link {
  flex: none;
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 14px 7px 8px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--ink-soft);
  font-size: 13px;
  text-decoration: none;
  white-space: nowrap;
  transition: border-color .15s, color .15s;
}
.l4-step-link:hover { border-color: var(--teal); color: var(--teal-dark); }
.l4-step-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 20px; height: 20px;
  border-radius: 50%;
  background: var(--teal);
  color: #fff;
  font-size: 11px;
  font-weight: 700;
  font-family: "IBM Plex Mono", monospace;
}

/* --- Hero --- */
.l4-hero {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 32px;
  align-items: center;
  padding: 28px 0 40px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 36px;
}
@media (max-width: 760px) {
  .l4-hero { grid-template-columns: 1fr; }
}
.l4-eyebrow {
  font-family: "IBM Plex Mono", monospace;
  font-size: 12px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--teal-dark);
  margin: 0 0 8px;
}
.l4-hero h1 {
  font-size: 30px;
  line-height: 1.15;
  margin: 0 0 12px;
  letter-spacing: -0.01em;
}
.l4-hero p {
  color: var(--ink-soft);
  font-size: 15px;
  line-height: 1.6;
  max-width: 46ch;
}
.l4-mantra {
  display: inline-flex;
  gap: 10px;
  margin-top: 16px;
  padding: 10px 16px;
  border-radius: 10px;
  background: #fff8e6;
  border: 1px solid #f0deab;
  font-weight: 600;
  font-size: 14px;
  color: #7a5b0c;
}

/* --- Sơ đồ chuyển electron (signature element) --- */
.l4-flow {
  position: relative;
  height: 200px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  overflow: hidden;
}
.l4-flow-atom {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 92px; height: 92px;
  border-radius: 50%;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 13px;
  text-align: center;
  line-height: 1.25;
}
.l4-flow-atom span { font-size: 11px; font-weight: 500; opacity: 0.85; }
.l4-flow-atom.give { left: 22px; background: var(--give-bg); border: 2px solid var(--give); color: var(--give); }
.l4-flow-atom.take { right: 22px; background: var(--take-bg); border: 2px solid var(--take); color: var(--take); }
.l4-flow-path {
  position: absolute;
  left: 108px; right: 108px; top: 50%;
  height: 2px;
  background: repeating-linear-gradient(90deg, var(--ink-soft) 0 6px, transparent 6px 12px);
  opacity: 0.35;
}
.l4-flow-e {
  position: absolute;
  top: 50%;
  width: 22px; height: 22px;
  margin-top: -11px; margin-left: -11px;
  border-radius: 50%;
  background: var(--give);
  color: #fff;
  font-size: 11px;
  font-family: "IBM Plex Mono", monospace;
  display: flex; align-items: center; justify-content: center;
  animation: l4-e-travel 2.6s ease-in-out infinite;
}
.l4-flow-e.e2 { animation-delay: 1.3s; }
.l4-flow-label {
  position: absolute;
  bottom: 10px; left: 0; right: 0;
  text-align: center;
  font-size: 11px;
  color: var(--ink-soft);
  font-family: "IBM Plex Mono", monospace;
}
@keyframes l4-e-travel {
  0%   { left: 22%; opacity: 0; }
  10%  { opacity: 1; }
  90%  { opacity: 1; }
  100% { left: 78%; opacity: 0; }
}
@media (prefers-reduced-motion: reduce) {
  .l4-flow-e { animation: none; left: 50%; opacity: 1; }
}

/* --- Section chung --- */
.l4-section { margin-bottom: 56px; scroll-margin-top: 70px; }
.l4-section-head { margin-bottom: 20px; }
.l4-kicker {
  font-family: "IBM Plex Mono", monospace;
  font-size: 12px;
  color: var(--teal-dark);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin: 0 0 4px;
}
.l4-section h2 { font-size: 22px; margin: 0 0 6px; }
.l4-section-sub { color: var(--ink-soft); font-size: 14.5px; line-height: 1.6; margin: 0; max-width: 68ch; }

/* --- Cặp thẻ khái niệm chất khử / chất oxi hóa --- */
.l4-concept-pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin: 22px 0;
}
@media (max-width: 640px) { .l4-concept-pair { grid-template-columns: 1fr; } }
.l4-concept-card {
  border-radius: 12px;
  padding: 18px 20px;
  border: 1.5px solid;
}
.l4-concept-card.give { background: var(--give-bg); border-color: var(--give-line); }
.l4-concept-card.take { background: var(--take-bg); border-color: var(--take-line); }
.l4-concept-card h3 {
  margin: 0 0 6px; font-size: 15px; display: flex; align-items: center; gap: 8px;
}
.l4-concept-card.give h3 { color: var(--give); }
.l4-concept-card.take h3 { color: var(--take); }
.l4-concept-card p { margin: 0; font-size: 13.5px; line-height: 1.55; color: var(--ink); }
.l4-concept-card .l4-tag {
  display: inline-block; margin-top: 10px;
  font-family: "IBM Plex Mono", monospace; font-size: 11.5px;
  padding: 2px 8px; border-radius: 999px; background: rgba(0,0,0,0.05);
}

/* --- Ô nhập liệu tương tác (dùng chung mọi giai đoạn) --- */
.l4-tool {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 20px;
}
.l4-tool-label {
  font-size: 12.5px; font-weight: 600; color: var(--ink-soft);
  margin-bottom: 8px; display: block;
}
.l4-examples {
  display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0 0;
}
.l4-example-chip {
  font-family: "IBM Plex Mono", monospace;
  font-size: 12px;
  padding: 5px 10px;
  border-radius: 7px;
  background: #eef3f0;
  border: 1px solid var(--line);
  color: var(--ink-soft);
  cursor: pointer;
}
.l4-example-chip:hover { border-color: var(--teal); color: var(--teal-dark); }

/* --- Kết quả số oxi hóa (giai đoạn 1) --- */
.l4-ox-formula {
  font-family: "IBM Plex Mono", monospace;
  font-size: 22px;
  margin: 16px 0 14px;
  display: flex; align-items: baseline; gap: 2px; flex-wrap: wrap;
}
.l4-ox-el { position: relative; padding: 2px 3px; border-radius: 5px; }
.l4-ox-el.give { background: var(--give-bg); color: var(--give); }
.l4-ox-el.take { background: var(--take-bg); color: var(--take); }
.l4-ox-el.zero { background: #eef3f0; color: var(--ink-soft); }
.l4-steps {
  list-style: none; margin: 14px 0 0; padding: 0;
  display: flex; flex-direction: column; gap: 6px;
}
.l4-steps li {
  font-size: 13.5px; line-height: 1.55; color: var(--ink);
  padding-left: 18px; position: relative;
}
.l4-steps li::before {
  content: "→"; position: absolute; left: 0; color: var(--teal); font-weight: 700;
}

/* --- Giai đoạn 2: quy trình 4 bước cân bằng electron --- */
.l4-procedure {
  counter-reset: l4step;
  display: grid; gap: 10px; margin: 20px 0 28px;
}
.l4-procedure li {
  list-style: none;
  counter-increment: l4step;
  display: flex; gap: 14px; align-items: flex-start;
  padding: 12px 14px;
  background: var(--card); border: 1px solid var(--line); border-radius: 10px;
}
.l4-procedure li::before {
  content: counter(l4step);
  flex: none;
  width: 26px; height: 26px; border-radius: 50%;
  background: var(--teal); color: #fff;
  display: flex; align-items: center; justify-content: center;
  font-family: "IBM Plex Mono", monospace; font-size: 13px; font-weight: 700;
}
.l4-procedure strong { display: block; font-size: 13.5px; margin-bottom: 2px; }
.l4-procedure span { font-size: 13px; color: var(--ink-soft); line-height: 1.5; }

.l4-process-cards {
  display: grid; gap: 10px; margin: 16px 0;
}
.l4-process-card {
  border-radius: 10px; padding: 12px 16px; border: 1.5px solid;
  font-family: "IBM Plex Mono", monospace; font-size: 13.5px;
  display: flex; align-items: center; justify-content: space-between; gap: 10px; flex-wrap: wrap;
}
.l4-process-card.give { background: var(--give-bg); border-color: var(--give-line); color: var(--give); }
.l4-process-card.take { background: var(--take-bg); border-color: var(--take-line); color: var(--take); }
.l4-process-card .l4-pc-label {
  font-family: "Be Vietnam Pro", system-ui, sans-serif;
  font-size: 11.5px; font-weight: 700; text-transform: uppercase; letter-spacing: 0.04em;
  opacity: 0.85;
}
.l4-lcm-note {
  background: #fff8e6; border: 1px solid #f0deab; border-radius: 10px;
  padding: 12px 16px; font-size: 13.5px; color: #7a5b0c; margin: 12px 0;
}

/* --- Kết quả cuối / bảng đếm --- */
.l4-final { margin-top: 18px; }
.l4-check-table td.ok::after { content: " ✓"; }
.l4-check-table td.bad::after { content: " ✗"; }

/* --- Giai đoạn 3: các dạng bài --- */
.l4-pattern-grid {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 14px; margin: 20px 0;
}
@media (max-width: 820px) { .l4-pattern-grid { grid-template-columns: 1fr; } }
.l4-pattern-card {
  background: var(--card); border: 1px solid var(--line); border-radius: 12px;
  padding: 16px; display: flex; flex-direction: column; gap: 10px;
}
.l4-pattern-card h3 { font-size: 14.5px; margin: 0; }
.l4-pattern-card p { font-size: 13px; color: var(--ink-soft); line-height: 1.5; margin: 0; flex: 1; }
.l4-pattern-eq {
  font-family: "IBM Plex Mono", monospace; font-size: 12.5px;
  background: #eef3f0; border-radius: 6px; padding: 8px 10px; word-break: break-word;
}
.l4-pattern-card button { align-self: flex-start; }

/* --- Giai đoạn 4: bảo toàn electron --- */
.l4-balance-visual {
  display: flex; align-items: center; justify-content: center; gap: 18px;
  padding: 22px; background: var(--card); border: 1px solid var(--line); border-radius: 14px;
  margin: 18px 0;
}
.l4-balance-box {
  flex: 1; max-width: 260px;
  border-radius: 10px; padding: 14px 16px; text-align: center;
  font-family: "IBM Plex Mono", monospace; font-size: 13.5px;
}
.l4-balance-box.give { background: var(--give-bg); color: var(--give); border: 1.5px solid var(--give-line); }
.l4-balance-box.take { background: var(--take-bg); color: var(--take); border: 1.5px solid var(--take-line); }
.l4-balance-eq-sign { font-size: 22px; font-weight: 700; color: var(--ink-soft); }

.l4-worked-example {
  background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 20px; margin: 18px 0;
}
.l4-worked-example h3 { font-size: 14.5px; margin: 0 0 10px; }
.l4-worked-example .l4-eq-highlight {
  font-family: "IBM Plex Mono", monospace; font-size: 15px;
  background: #eef3f0; border-radius: 8px; padding: 10px 14px; margin: 10px 0;
}

.l4-practice {
  background: var(--card); border: 1px solid var(--line); border-radius: 14px; padding: 20px; margin-top: 18px;
}
.l4-practice-note {
  font-size: 12px; color: var(--ink-soft); margin: 0 0 14px; font-style: italic;
}
.l4-metal-row {
  display: grid; grid-template-columns: 1fr 110px; gap: 10px; margin-bottom: 10px; align-items: center;
}
.l4-practice-result {
  margin-top: 16px; padding: 14px 16px; border-radius: 10px;
  background: #eef3f0; font-family: "IBM Plex Mono", monospace; font-size: 13.5px; line-height: 1.7;
}
.l4-practice-result strong { color: var(--teal-dark); }

/* --- Hộp lỗi dùng chung --- */
.l4-error {
  color: var(--error); background: #fdeeee; border: 1px solid #f0c4c4;
  border-radius: 8px; padding: 10px 14px; font-size: 13.5px; margin-top: 10px;
}