:root {
  --blue: #2878f0;
  --blue-dark: #165fd5;
  --blue-soft: #eaf3ff;
  --navy: #142b50;
  --muted: #73819a;
  --line: #e5eaf1;
  --cream: #fffdf8;
  --yellow: #ffbd16;
  --yellow-dark: #f3a800;
  --green: #27b76b;
  --coral: #ff756d;
  --shadow: 0 18px 55px rgba(27, 54, 94, 0.12);
}

* {
  box-sizing: border-box;
}

html {
  min-width: 320px;
  background: var(--cream);
}

body {
  margin: 0;
  min-height: 100vh;
  color: var(--navy);
  font-family: "PingFang SC", "Microsoft YaHei", "Noto Sans SC", system-ui, sans-serif;
  background:
    radial-gradient(circle at 8% 86%, rgba(146, 199, 255, 0.32), transparent 19rem),
    radial-gradient(circle at 92% 82%, rgba(255, 222, 119, 0.2), transparent 18rem),
    linear-gradient(180deg, #fffefb 0%, #f8fbff 100%);
}

button,
input {
  font: inherit;
}

button {
  color: inherit;
}

button:focus-visible,
input:focus-visible,
a:focus-visible {
  outline: 4px solid rgba(40, 120, 240, 0.23);
  outline-offset: 3px;
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.site-header {
  position: relative;
  z-index: 10;
  display: grid;
  grid-template-columns: minmax(230px, 1fr) auto minmax(230px, 1fr);
  align-items: center;
  min-height: 96px;
  padding: 0 4.5vw;
  background: rgba(255, 255, 255, 0.88);
  border-bottom: 1px solid rgba(20, 43, 80, 0.07);
  box-shadow: 0 8px 25px rgba(31, 54, 91, 0.06);
  backdrop-filter: blur(14px);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 14px;
  width: max-content;
  color: var(--navy);
  font-size: clamp(1.35rem, 2.1vw, 2rem);
  font-weight: 800;
  letter-spacing: 0.04em;
  text-decoration: none;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 54px;
  height: 60px;
  color: white;
  font-size: 2rem;
  line-height: 1;
  background: linear-gradient(145deg, #438ff8, #1d68da);
  border: 4px solid white;
  border-radius: 15px;
  box-shadow: 0 7px 0 #174fa7, 0 10px 20px rgba(30, 98, 205, 0.23);
  transform: rotate(-6deg);
}

.main-nav {
  display: flex;
  align-items: center;
  gap: 10px;
}

.nav-item {
  padding: 14px 25px;
  background: transparent;
  border: 0;
  border-radius: 14px;
  font-weight: 700;
  cursor: pointer;
  transition: 180ms ease;
}

.nav-item:hover {
  color: var(--blue);
  background: var(--blue-soft);
}

.nav-item.active {
  color: var(--blue);
  background: #edf4ff;
}

.streak {
  justify-self: end;
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 1rem;
  font-weight: 600;
}

.streak span {
  font-size: 1.8rem;
}

.streak strong {
  color: var(--blue);
  font-size: 1.35rem;
}

main {
  width: min(1320px, 92vw);
  margin: 0 auto;
  padding: 40px 0 56px;
}

.view {
  display: none;
}

.view.active {
  display: block;
  animation: view-in 260ms ease;
}

@keyframes view-in {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.practice-shell {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 230px;
  align-items: stretch;
  gap: 28px;
}

.practice-card,
.secondary-card {
  overflow: hidden;
  background: rgba(255, 255, 255, 0.95);
  border: 1px solid rgba(20, 43, 80, 0.08);
  border-radius: 26px;
  box-shadow: var(--shadow);
}

.practice-card {
  padding: 30px 38px 0;
}

.grade-tabs {
  display: grid;
  grid-template-columns: repeat(6, 1fr);
  overflow: hidden;
  border: 1px solid #dbe3ed;
  border-radius: 17px;
}

.grade-tab {
  min-height: 62px;
  padding: 10px;
  background: #fff;
  border: 0;
  border-right: 1px solid #e5eaf1;
  font-weight: 700;
  cursor: pointer;
  transition: 160ms ease;
}

.grade-tab:last-child {
  border-right: 0;
}

.grade-tab:hover {
  background: #f5f9ff;
}

.grade-tab.active {
  color: white;
  background: linear-gradient(145deg, #3384f5, #1b64dc);
  box-shadow: 0 7px 16px rgba(28, 103, 220, 0.25);
}

.level-row {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 28px;
  padding: 26px 8px 20px;
}

.eyebrow {
  margin: 0 0 10px;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.12em;
}

.level-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.level-chip {
  padding: 9px 20px;
  color: #51617c;
  background: white;
  border: 1px solid #dce4ed;
  border-radius: 999px;
  font-weight: 650;
  cursor: pointer;
}

.level-chip:hover {
  color: var(--blue);
  border-color: #9cc5ff;
}

.level-chip.active {
  color: white;
  background: var(--blue);
  border-color: var(--blue);
}

.goal-block {
  width: 220px;
  flex: 0 0 auto;
}

.goal-copy {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 8px;
  font-size: 0.88rem;
}

.goal-copy strong {
  font-size: 1rem;
}

.progress-track {
  height: 9px;
  overflow: hidden;
  background: #e6ebf2;
  border-radius: 999px;
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, #1686f4, #3b75f1);
  border-radius: inherit;
  transition: width 300ms ease;
}

.divider {
  height: 1px;
  background: var(--line);
}

.question-zone {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 510px;
  padding: 28px 3vw 26px;
}

.question-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  min-height: 38px;
}

.question-tag {
  padding: 7px 13px;
  color: var(--blue-dark);
  font-size: 0.84rem;
  font-weight: 700;
  background: var(--blue-soft);
  border-radius: 999px;
}

.feedback {
  min-height: 34px;
  padding: 7px 13px;
  color: var(--green);
  font-size: 0.9rem;
  font-weight: 750;
  border-radius: 999px;
  transition: 180ms ease;
}

.feedback:not(:empty) {
  background: #eaf9f0;
}

.feedback.error {
  color: #e45151;
  background: #fff0ef;
}

.question {
  display: grid;
  place-items: center;
  min-height: 154px;
  padding: 22px 0 12px;
  color: #12294d;
  font-size: clamp(3.1rem, 6vw, 5.5rem);
  font-weight: 850;
  line-height: 1.08;
  letter-spacing: 0.02em;
  text-align: center;
}

.question.bump {
  animation: bump 280ms ease;
}

@keyframes bump {
  0% { transform: scale(0.94); opacity: 0.5; }
  65% { transform: scale(1.03); }
  100% { transform: scale(1); opacity: 1; }
}

.answer-row {
  display: grid;
  grid-template-columns: minmax(180px, 360px) 190px;
  gap: 18px;
  width: min(100%, 570px);
}

.answer-input {
  min-width: 0;
  height: 66px;
  padding: 0 26px;
  color: var(--navy);
  font-size: 1.35rem;
  font-weight: 700;
  background: white;
  border: 3px solid var(--blue);
  border-radius: 18px;
  transition: 160ms ease;
}

.answer-input::placeholder {
  color: #b7bdc8;
}

.answer-input.shake {
  border-color: var(--coral);
  animation: shake 320ms ease;
}

@keyframes shake {
  25% { transform: translateX(-8px); }
  50% { transform: translateX(7px); }
  75% { transform: translateX(-4px); }
}

.button {
  border: 0;
  border-radius: 17px;
  font-weight: 800;
  cursor: pointer;
}

.button-primary {
  color: white;
  font-size: 1.2rem;
  background: linear-gradient(150deg, #398cff, #1c67dd);
  box-shadow: 0 8px 0 #1658c0, 0 13px 22px rgba(28, 103, 221, 0.24);
  transition: 120ms ease;
}

.button-primary:hover {
  filter: brightness(1.05);
  transform: translateY(-1px);
}

.button-primary:active {
  box-shadow: 0 3px 0 #1658c0, 0 8px 15px rgba(28, 103, 221, 0.2);
  transform: translateY(5px);
}

.button:disabled,
.answer-input:disabled {
  cursor: not-allowed;
  opacity: 0.58;
}

.answer-hint {
  margin: 13px 0 23px;
  color: #9aa4b4;
  font-size: 0.82rem;
}

.new-question-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 16px;
  min-width: min(100%, 380px);
  min-height: 72px;
  padding: 14px 32px;
  color: white;
  font-size: clamp(1.25rem, 2.1vw, 1.65rem);
  font-weight: 850;
  letter-spacing: 0.04em;
  background: linear-gradient(180deg, #ffca28, #ffb70e);
  border: 0;
  border-radius: 22px;
  box-shadow: 0 8px 0 var(--yellow-dark), 0 14px 28px rgba(241, 172, 0, 0.25);
  cursor: pointer;
  transition: 120ms ease;
}

.new-question-button:hover {
  filter: brightness(1.03);
  transform: translateY(-2px);
}

.new-question-button:active {
  box-shadow: 0 3px 0 var(--yellow-dark), 0 8px 18px rgba(241, 172, 0, 0.22);
  transform: translateY(5px);
}

.spark {
  font-size: 1.7rem;
}

.new-question-hint {
  margin: 17px 0 0;
  color: var(--muted);
  font-size: 0.94rem;
  font-weight: 600;
}

.stats-row {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin: 0 -38px;
  padding: 24px 38px;
  border-top: 1px solid var(--line);
}

.stat-item {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 11px;
  min-height: 48px;
  padding: 0 18px;
  font-weight: 650;
  border-right: 1px solid var(--line);
}

.stat-item:last-child {
  border-right: 0;
}

.stat-item strong {
  color: var(--blue);
  font-size: 1.65rem;
}

.stat-item:nth-child(2) strong { color: var(--green); }
.stat-item:nth-child(3) strong { color: #f6a700; }

.stat-icon {
  font-size: 2rem;
  font-weight: 800;
}

.blue { color: var(--blue); }
.green { color: var(--green); }
.yellow { color: var(--yellow-dark); }

.mascot-panel {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 520px;
  overflow: hidden;
  padding: 30px 16px;
  background:
    radial-gradient(circle at 50% 76%, rgba(121, 186, 255, 0.23), transparent 8rem),
    rgba(255, 255, 255, 0.47);
  border-radius: 28px;
}

.mascot-panel::after {
  content: "";
  position: absolute;
  right: -55px;
  bottom: -45px;
  width: 180px;
  height: 120px;
  background: #dfefff;
  border-radius: 50%;
  z-index: -1;
}

.mascot-panel p {
  max-width: 180px;
  margin: 30px 0 0;
  color: #51617c;
  font-weight: 700;
  line-height: 1.7;
  text-align: center;
}

.floating-star {
  position: absolute;
  top: 105px;
  left: 20px;
  color: var(--yellow);
  font-size: 4.7rem;
  line-height: 1;
  filter: drop-shadow(0 7px 0 #f1a801);
  transform: rotate(-10deg);
  animation: float 2.4s ease-in-out infinite;
}

@keyframes float {
  50% { transform: translateY(-10px) rotate(-6deg); }
}

.pencil {
  position: relative;
  width: 88px;
  height: 290px;
  margin-top: 48px;
  filter: drop-shadow(0 16px 15px rgba(59, 69, 85, 0.16));
  transform: rotate(7deg);
}

.eraser {
  width: 88px;
  height: 50px;
  background: linear-gradient(#ff8a83, #ef6b6b);
  border-radius: 32px 32px 10px 10px;
  border-bottom: 12px solid #cdd6e0;
}

.pencil-body {
  position: relative;
  width: 76px;
  height: 185px;
  margin: 0 auto;
  background: linear-gradient(90deg, #f8ad00, #ffd443 45%, #f2a600);
}

.eye {
  position: absolute;
  top: 50px;
  width: 10px;
  height: 18px;
  background: #2d2930;
  border-radius: 50%;
}

.eye.left { left: 20px; }
.eye.right { right: 20px; }

.smile {
  position: absolute;
  top: 82px;
  left: 50%;
  width: 30px;
  height: 17px;
  border-bottom: 6px solid #4b2b2b;
  border-radius: 0 0 50% 50%;
  transform: translateX(-50%);
}

.pencil-tip {
  width: 0;
  height: 0;
  margin: 0 auto;
  border-top: 55px solid #eac79c;
  border-left: 38px solid transparent;
  border-right: 38px solid transparent;
}

.pencil-tip::after {
  content: "";
  position: absolute;
  left: 50%;
  bottom: -1px;
  width: 0;
  height: 0;
  border-top: 17px solid #263142;
  border-left: 10px solid transparent;
  border-right: 10px solid transparent;
  transform: translate(-50%, 55px);
}

.secondary-view {
  padding: 10px 0;
}

.secondary-card {
  min-height: 580px;
  padding: 36px;
}

.section-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 28px;
}

.section-heading h2 {
  margin: 0;
  font-size: 2rem;
}

.text-button {
  padding: 10px 16px;
  color: #e45151;
  font-weight: 700;
  background: #fff1f0;
  border: 0;
  border-radius: 12px;
  cursor: pointer;
}

.mistakes-list {
  display: grid;
  gap: 12px;
}

.mistake-item {
  display: grid;
  grid-template-columns: 1fr auto auto;
  align-items: center;
  gap: 18px;
  padding: 18px 22px;
  background: #f8faff;
  border: 1px solid #e6ebf2;
  border-radius: 16px;
}

.mistake-item strong {
  font-size: 1.2rem;
}

.mistake-answer {
  color: #e45151;
}

.right-answer {
  color: var(--green);
}

.empty-state {
  display: grid;
  place-items: center;
  min-height: 380px;
  color: var(--muted);
  font-weight: 650;
  text-align: center;
}

.empty-state span {
  display: block;
  margin-bottom: 14px;
  font-size: 4rem;
}

.report-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 20px;
}

.report-tile {
  display: flex;
  flex-direction: column;
  min-height: 230px;
  padding: 28px;
  border-radius: 22px;
}

.report-tile span {
  font-weight: 750;
}

.report-tile strong {
  margin: 26px 0 18px;
  font-size: 4rem;
  line-height: 1;
}

.report-tile small {
  margin-top: auto;
  color: var(--muted);
}

.blue-tile { background: #eaf3ff; }
.green-tile { background: #eaf9f0; }
.yellow-tile { background: #fff8df; }

.celebration {
  position: fixed;
  inset: 0;
  z-index: 50;
  pointer-events: none;
  overflow: hidden;
}

.confetti {
  position: absolute;
  top: -20px;
  width: 10px;
  height: 16px;
  border-radius: 3px;
  animation: confetti-fall 1000ms ease-in forwards;
}

@keyframes confetti-fall {
  to {
    transform: translate3d(var(--drift), 105vh, 0) rotate(620deg);
    opacity: 0;
  }
}

@media (max-width: 1040px) {
  .site-header {
    grid-template-columns: auto 1fr auto;
    padding: 0 3vw;
  }

  .brand span:last-child { display: none; }
  .main-nav { justify-content: center; }
  .practice-shell { grid-template-columns: 1fr; }
  .mascot-panel { display: none; }
}

@media (max-width: 720px) {
  .site-header {
    grid-template-columns: auto 1fr;
    min-height: 76px;
  }

  .brand-mark {
    width: 44px;
    height: 49px;
    font-size: 1.6rem;
  }

  .main-nav {
    justify-content: flex-end;
    gap: 2px;
  }

  .nav-item {
    padding: 10px 9px;
    font-size: 0.84rem;
  }

  .streak { display: none; }
  main { width: min(94vw, 620px); padding-top: 22px; }
  .practice-card { padding: 16px 16px 0; border-radius: 20px; }

  .grade-tabs {
    grid-template-columns: repeat(3, 1fr);
  }

  .grade-tab {
    min-height: 48px;
    border-bottom: 1px solid #e5eaf1;
  }

  .level-row {
    align-items: stretch;
    flex-direction: column;
    padding: 20px 2px 15px;
  }

  .goal-block { width: 100%; }
  .question-zone { min-height: 460px; padding: 20px 0; }
  .question-heading { align-items: flex-start; gap: 8px; }
  .question { min-height: 130px; font-size: clamp(2.7rem, 14vw, 4.2rem); }

  .answer-row {
    grid-template-columns: 1fr;
    gap: 11px;
  }

  .answer-input,
  .button-primary { height: 58px; }
  .new-question-button { min-height: 63px; }

  .stats-row {
    grid-template-columns: 1fr;
    gap: 12px;
    margin: 0 -16px;
    padding: 20px 16px;
  }

  .stat-item {
    justify-content: flex-start;
    border-right: 0;
  }

  .secondary-card { padding: 24px 18px; }
  .report-grid { grid-template-columns: 1fr; }
  .report-tile { min-height: 180px; }

  .mistake-item {
    grid-template-columns: 1fr;
    gap: 7px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}