* {
  box-sizing: border-box;
}

:root {
  --body-bg: #f5f7fb;
  --text-main: #15213a;
  --panel-left-bg: #ffffff;
  --panel-right-bg: #f8faff;
  --border: #c7d2e8;
  --border-soft: #d7deeb;
  --surface: #ffffff;
  --surface-alt: #f3f6ff;
  --hover: #dce7ff;
}

body.dark-mode {
  --body-bg: #121722;
  --text-main: #edf2ff;
  --panel-left-bg: #171d2a;
  --panel-right-bg: #151b28;
  --border: #3c4a66;
  --border-soft: #324058;
  --surface: #1c2434;
  --surface-alt: #26344d;
  --hover: #334a72;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  background: var(--body-bg);
  color: var(--text-main);
}

.layout {
  --left-panel-width: 50%;
  display: flex;
  min-height: 100vh;
}

.panel {
  padding: 1.25rem;
}

.left-panel {
  width: var(--left-panel-width);
  min-width: 280px;
  background: var(--panel-left-bg);
  overflow: hidden;
}

.right-panel {
  flex: 1;
  min-width: 280px;
  background: var(--panel-right-bg);
  overflow: hidden;
}

.panel-divider {
  width: 10px;
  cursor: col-resize;
  background: var(--panel-right-bg);
  border-left: 1px solid var(--border-soft);
  border-right: 1px solid var(--border-soft);
  position: relative;
}

.panel-divider::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 2px;
  height: 44px;
  transform: translate(-50%, -50%);
  border-radius: 2px;
  background: var(--border);
}

h1,
h2 {
  margin: 0 0 0.75rem;
}

#sourceText {
  width: 100%;
  height: calc(100vh - 5rem);
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  padding: 1rem;
  resize: none;
  font-size: 1.4rem;
  line-height: 1.8;
  background: var(--surface);
  color: var(--text-main);
}

.char-container {
  height: 40vh;
  max-height: 32rem;
  min-height: 12rem;
  padding: 0.9rem;
  line-height: 2;
  overflow-y: auto;
  color: var(--text-main);
}

.char {
  border: none;
  background: transparent;
  color: var(--text-main);
  font-size: var(--char-font-size, 1.8rem);
  padding: 0.2rem 0.25rem 0.3rem;
  margin: 0.08rem;
  border-radius: 0.35rem;
  cursor: pointer;
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  justify-content: flex-start;
  min-width: 2.2em;
  line-height: 1.1;
}

.char:hover,
.char.active {
  background: var(--hover);
}

.char.space {
  cursor: default;
  min-width: 1.2em;
}

.char-hanzi {
  display: block;
}

.char-pinyin {
  display: block;
  margin-top: 0.12rem;
  font-size: 0.38em;
  opacity: 0.85;
}

.char-box {
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  background: var(--surface);
}

.char-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.char-tools-row {
  margin-bottom: 0.45rem;
}

.header-controls {
  display: flex;
  gap: 0.35rem;
}

.char-controls {
  display: flex;
  gap: 0.35rem;
}

.header-controls button,
.char-controls button {
  border: 1px solid var(--border);
  background: var(--surface-alt);
  color: var(--text-main);
  border-radius: 0.35rem;
  padding: 0.2rem 0.45rem;
  cursor: pointer;
  font-size: 0.9rem;
}

.header-controls button:hover,
.char-controls button:hover {
  background: var(--hover);
}

.stroke-panel {
  margin-top: 1rem;
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  background: var(--surface);
  padding: 0.75rem;
  min-height: 14rem;
}

#strokeStatus {
  margin: 0 0 0.5rem;
}

#strokeImage {
  width: 100%;
  max-width: 336px;
  height: auto;
  display: block;
}

body.dark-mode #strokeImage {
  filter: invert(1);
}

@media (max-width: 900px) {
  .layout {
    display: block;
  }

  .left-panel {
    width: 100%;
    border-bottom: 1px solid var(--border-soft);
  }

  .right-panel {
    width: 100%;
  }

  .panel-divider {
    display: none;
  }

  #sourceText {
    height: 16rem;
  }
}