:root {
  --background: #ffffff;
  --card: #ffffff;
  --text: #1f2933;
  --muted: #5f6b76;
  --border: #d8dee4;
  --accent: #234f7d;
  --soft-accent: #eaf1f8;
  --soft-null: #fff8e6;
  --null-text: #765b12;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--background);
  color: var(--text);
  font-family: Georgia, "Times New Roman", serif;
  line-height: 1.5;
}

.join-explorer {
  padding: 18px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--card);
}

.activity-intro {
  margin-bottom: 14px;
}

.activity-intro h2 {
  margin: 0 0 6px;
  font-size: 1.25rem;
}

.activity-intro p {
  margin: 0;
  color: var(--muted);
}

.controls {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  align-items: end;
  margin: 16px 0;
}

.control-group label {
  display: block;
  margin-bottom: 5px;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 0.85rem;
  font-weight: 700;
}

select {
  width: 100%;
  padding: 9px 10px;
  border: 1px solid var(--border);
  border-radius: 9px;
  background: #ffffff;
  color: var(--text);
  font-size: 0.95rem;
}

button {
  border: 1px solid var(--accent);
  border-radius: 999px;
  padding: 10px 16px;
  background: var(--accent);
  color: #ffffff;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 0.95rem;
  font-weight: 700;
  cursor: pointer;
}

button:hover {
  opacity: 0.92;
}

.explanation-box {
  margin: 0 0 16px;
  padding: 12px 14px;
  border-left: 4px solid var(--accent);
  border-radius: 10px;
  background: var(--soft-accent);
}

.explanation-box p {
  margin: 0;
}

.tables-area {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
  margin-bottom: 16px;
}

.source-table-card,
.result-card {
  min-width: 0;
}

.source-table-card h3,
.result-card h3 {
  margin: 0 0 8px;
  font-size: 1rem;
}

.table-scroll {
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: 10px;
}

table {
  width: 100%;
  min-width: 520px;
  border-collapse: collapse;
  background: #ffffff;
}

th,
td {
  padding: 8px 10px;
  border: 1px solid var(--border);
  text-align: left;
  white-space: nowrap;
  font-size: 0.92rem;
}

th {
  background: #f7f7f5;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 0.8rem;
  font-weight: 700;
}

tr:nth-child(even) td {
  background: #fbfbfa;
}

th {
  background: #f7f7f5;
  font-family: Arial, Helvetica, sans-serif;
  font-size: 0.8rem;
  font-weight: 700;
}

tr:last-child td {
  border-bottom: none;
}

.null-cell {
  background: var(--soft-null);
  color: var(--null-text);
  font-family: Arial, Helvetica, sans-serif;
  font-size: 0.78rem;
  font-weight: 700;
}

.empty-message {
  margin: 0;
  padding: 12px;
  color: var(--muted);
}

@media (max-width: 800px) {
  .join-explorer {
    padding: 14px;
  }

  .controls,
  .tables-area {
    grid-template-columns: 1fr;
  }

}