:root {
  --color-primary: #4f7df3;
  --color-primary-dark: #3a63d6;
  --color-bg: #f7f8fb;
  --color-surface: #ffffff;
  --color-text: #1f2430;
  --color-text-muted: #6b7280;
  --color-border: #e5e7eb;
  --color-danger: #e0555a;
  --radius: 12px;
  --spacing: 16px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Microsoft YaHei", sans-serif;
  background: var(--color-bg);
  color: var(--color-text);
  padding-bottom: 72px;
}

.banner {
  padding: 10px var(--spacing);
  font-size: 14px;
  text-align: center;
}
.banner-error {
  background: #fdecea;
  color: var(--color-danger);
}

.topnav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: var(--spacing);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
}
.app-title {
  font-size: 18px;
  margin: 0;
}
.topnav .tabs {
  display: none;
  gap: 8px;
}

main {
  max-width: 640px;
  margin: 0 auto;
  padding: var(--spacing);
}

.tab-panel[hidden] { display: none; }

.tab-btn {
  border: none;
  background: transparent;
  padding: 8px 16px;
  border-radius: var(--radius);
  font-size: 15px;
  color: var(--color-text-muted);
  cursor: pointer;
}
.tab-btn.active {
  background: var(--color-primary);
  color: #fff;
}

.bottom-nav {
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding: 6px max(6px, env(safe-area-inset-bottom));
}
.bottom-nav .tab-btn {
  flex: 1;
  min-height: 44px;
}

@media (min-width: 768px) {
  .topnav .tabs { display: flex; }
  .bottom-nav { display: none; }
  body { padding-bottom: 0; }
}

.form-row {
  margin-bottom: 12px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.form-row label {
  font-size: 14px;
  color: var(--color-text-muted);
}
.required { color: var(--color-danger); }

input[type="text"], textarea {
  padding: 10px 12px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 15px;
  min-height: 44px;
  font-family: inherit;
}
textarea { min-height: 60px; resize: vertical; }
input.invalid { border-color: var(--color-danger); }

.form-actions {
  display: flex;
  gap: 8px;
  margin-top: 8px;
}

.btn {
  min-height: 44px;
  padding: 0 16px;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  font-size: 15px;
  cursor: pointer;
}
.btn-primary {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: #fff;
}
.btn-secondary { color: var(--color-text-muted); }
.btn-small {
  min-height: 36px;
  padding: 0 12px;
  font-size: 13px;
}
.btn-delete { color: var(--color-danger); }

.word-list {
  list-style: none;
  margin: 16px 0 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.word-item {
  background: var(--color-surface);
  border-radius: var(--radius);
  padding: 12px 14px;
  border: 1px solid var(--color-border);
}
.word-item-main {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
}
.word-en { font-weight: 600; }
.word-zh { color: var(--color-text-muted); }
.word-visible { font-weight: 600; }
.word-example {
  margin: 8px 0 0;
  font-size: 14px;
  color: var(--color-text-muted);
  font-style: italic;
}
.word-item-actions {
  display: flex;
  gap: 8px;
  margin-top: 10px;
}

.empty-state {
  text-align: center;
  color: var(--color-text-muted);
  padding: 32px 0;
}

.search-input {
  width: 100%;
  padding: 10px 12px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  font-size: 15px;
  min-height: 44px;
}

.study-toggle {
  display: flex;
  gap: 8px;
  margin-bottom: 16px;
}
.toggle-btn {
  flex: 1;
  min-height: 44px;
  border-radius: var(--radius);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-muted);
  font-size: 15px;
  cursor: pointer;
}
.toggle-btn.active {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: #fff;
}
.study-item { cursor: pointer; }
.word-hidden {
  background: #eceff3;
  color: var(--color-text-muted);
  border-radius: 6px;
  padding: 2px 10px;
  transition: background 0.2s ease, color 0.2s ease;
}
.word-hidden.revealed {
  background: transparent;
  color: var(--color-text);
  font-weight: 600;
  padding: 2px 0;
}
.study-example {
  transition: opacity 0.2s ease;
}