:root {
  --bg: #eef2f7;
  --panel: #ffffff;
  --ink: #1f2a37;
  --muted: #5b6774;
  --line: #d5dde7;
  --accent: #0c3e78;
  --accent-2: #17a2a3;
  --shadow: 0 18px 32px rgba(31, 42, 55, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Trebuchet MS", "Segoe UI", Arial, sans-serif;
  background:
    radial-gradient(circle at 15% 0%, #f7fbff 0%, #eef2f7 55%),
    linear-gradient(180deg, #eef2f7 0%, #e6ebf2 100%);
  color: var(--ink);
  min-height: 100vh;
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  padding: 0.9rem 1.2rem;
  border-bottom: 1px solid var(--line);
  background: #ffffffde;
  backdrop-filter: blur(3px);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-size: 1.5rem;
  color: #232e3f;
}

.brand-dot {
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: linear-gradient(135deg, var(--accent-2), #f1c40f);
}

.author {
  margin: 0;
  color: var(--muted);
}

.page {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1.2rem;
  display: grid;
  gap: 1rem;
}

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 14px;
  box-shadow: var(--shadow);
}

.intro {
  padding: 1.2rem 1.3rem;
}

.intro h1 {
  margin-top: 0;
  color: var(--accent);
}

.intro p,
.intro li {
  line-height: 1.45;
  font-size: 1.05rem;
}

.intro a {
  color: #0b56b6;
}

.activity-heading {
  padding: 1rem 1.2rem;
}

.activity-heading h2 {
  margin: 0 0 0.3rem;
  color: var(--accent);
}

.activity-heading p {
  margin: 0;
  color: #2f4258;
}

.workspace {
  display: grid;
  grid-template-columns: 1fr 1fr;
  overflow: hidden;
}

.pane {
  min-width: 0;
}

.pane + .pane {
  border-left: 1px solid var(--line);
}

.pane-header {
  padding: 0.7rem 0.9rem;
  border-bottom: 1px solid var(--line);
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.pane-header h2 {
  margin: 0;
  font-size: 1.15rem;
  color: #273449;
}

.actions {
  display: flex;
  gap: 0.5rem;
}

button {
  border: 0;
  border-radius: 8px;
  background: var(--accent);
  color: #fff;
  font-weight: 700;
  font-size: 0.9rem;
  padding: 0.5rem 0.75rem;
  cursor: pointer;
}

button.secondary {
  background: #4d6077;
}

button:hover {
  filter: brightness(1.08);
}

#html-editor {
  width: 100%;
  height: 460px;
  border: 0;
  padding: 1rem;
  resize: vertical;
  font-family: "Cascadia Code", "Consolas", monospace;
  font-size: 0.96rem;
  line-height: 1.45;
  color: #1d2631;
}

.task-instructions {
  padding: 1rem 1.1rem 1.2rem;
  background: #f8fbff;
}

.task-instructions h3 {
  margin: 0 0 0.5rem;
  color: #1e3553;
}

.task-instructions p {
  margin: 0.55rem 0;
  color: #243447;
  line-height: 1.4;
}

.task-instructions code {
  font-family: "Cascadia Code", "Consolas", monospace;
  background: #eef4ff;
  border: 1px solid #d8e3f7;
  border-radius: 4px;
  padding: 0.1rem 0.25rem;
}

.task-instructions pre {
  margin: 0.4rem 0 0.8rem;
  padding: 0.6rem 0.7rem;
  background: #eef4ff;
  border: 1px solid #d8e3f7;
  border-radius: 6px;
  overflow-x: auto;
}

.task-instructions pre code {
  background: transparent;
  border: 0;
  padding: 0;
  border-radius: 0;
}

.parsons-list {
  margin: 0;
  padding: 0.8rem 0.8rem 0.9rem 2.6rem;
  min-height: 420px;
  list-style: decimal;
  background: #fbfdff;
}

.parsons-line {
  margin: 0.34rem 0;
  border: 1px solid #cfd9e7;
  border-radius: 6px;
  background: #f4f8ff;
  padding: 0.45rem 0.6rem;
  font-family: "Cascadia Code", "Consolas", monospace;
  font-size: 0.92rem;
  cursor: grab;
}

.parsons-line.dragging {
  opacity: 0.45;
}

.feedback {
  margin: 0;
  padding: 0.65rem 0.9rem 0.9rem;
  border-top: 1px solid var(--line);
  font-weight: 700;
  color: #334963;
}

.feedback.ok {
  color: #0d6d3b;
}

.feedback.warn {
  color: #9a5a00;
}

#preview-frame {
  width: 100%;
  height: 100%;
  min-height: 460px;
  border: 0;
  background: #fff;
}

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

@media (max-width: 900px) {
  .workspace {
    grid-template-columns: 1fr;
  }

  .pane + .pane {
    border-left: 0;
    border-top: 1px solid var(--line);
  }

  #html-editor,
  #preview-frame,
  #parsons-preview-frame {
    min-height: 320px;
  }

  .parsons-list {
    min-height: 300px;
  }
}

#parsons-preview-frame {
  width: 100%;
  height: 100%;
  min-height: 460px;
  border: 0;
  background: #fff;
}

.parsons-line.correct {
  background: #dff5e7;
  border-color: #53b87a;
  color: #134d2c;
}

.parsons-line.incorrect {
  background: #fde6e6;
  border-color: #e57a7a;
  color: #701717;
}