:root {
  --bg: #f7f7fb;
  --panel-bg: #ffffff;
  --border: #e0e0ea;
  --text: #26262f;
  --text-muted: #6b6b7a;
  --accent: #4f5fe0;
  --accent-dark: #3b47b8;
  --code-bg: #2b2d3a;
  --code-text: #e9e9f4;
  --error: #c0392b;
  --error-bg: #fbeceb;
  --success: #1f8a55;
  --success-bg: #e9f7f0;
  font-family: -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  line-height: 1.55;
}

.site-header {
  padding: 1.25rem 1.5rem 0.9rem;
  border-bottom: 1px solid var(--border);
  background: var(--panel-bg);
}

.site-header h1 {
  margin: 0;
  font-size: 1.3rem;
}

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

.profile-btn {
  width: 34px;
  height: 34px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text-muted);
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 0;
  flex-shrink: 0;
}

.profile-btn:hover {
  border-color: var(--accent);
  color: var(--accent-dark);
}

.profile-btn.filled {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

/* Tabs */

.tab-bar {
  display: flex;
  gap: 0.4rem;
  padding: 0.6rem 1.5rem 0;
  background: var(--panel-bg);
  border-bottom: 1px solid var(--border);
  overflow-x: auto;
}

.tab-btn {
  appearance: none;
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-size: 0.92rem;
  padding: 0.6rem 1rem;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  white-space: nowrap;
  flex-shrink: 0;
}

.tab-btn:hover {
  color: var(--text);
}

.tab-btn.active {
  color: var(--accent-dark);
  border-bottom-color: var(--accent);
  font-weight: 600;
}

.tab-content {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1.5rem;
}

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

/* Lesson tab */

.lesson-body {
  max-width: 760px;
}

.lesson-body h2:first-child {
  margin-top: 0;
}

.lesson-body code {
  background: #eceafc;
  color: var(--accent-dark);
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
  font-size: 0.9em;
}

.lesson-body pre {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 0.9rem 1rem;
  border-radius: 8px;
  overflow-x: auto;
  font-size: 0.9rem;
  margin: 0.5rem 0 1rem;
}

.lesson-body pre code {
  background: none;
  color: inherit;
  padding: 0;
}

.lesson-body details {
  margin: 0 0 0.7rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.15rem 0.9rem;
}

.lesson-body details[open] {
  padding-bottom: 0.7rem;
}

.lesson-body summary {
  cursor: pointer;
  padding: 0.7rem 0;
  font-weight: 600;
  color: var(--accent-dark);
  list-style: none;
}

.lesson-body summary::-webkit-details-marker {
  display: none;
}

.lesson-body summary::before {
  content: "▸ ";
  display: inline-block;
  width: 1em;
}

.lesson-body details[open] summary::before {
  content: "▾ ";
}

.lesson-body summary:hover {
  color: var(--accent);
}

/* Practice tab */

.practice-grid {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  grid-template-areas:
    "schema questions"
    "editor editor";
  gap: 1rem;
}

.practice-schema {
  grid-area: schema;
  min-width: 0;
}

.practice-questions {
  grid-area: questions;
  min-width: 0;
}

.practice-editor-section {
  grid-area: editor;
  min-width: 0;
}

@media (max-width: 760px) {
  .practice-grid {
    grid-template-columns: 1fr;
    grid-template-areas:
      "schema"
      "questions"
      "editor";
  }
}

.panel {
  background: var(--panel-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem;
}

.panel-title {
  margin: 0 0 0.6rem;
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
}

.panel-title.result-title {
  margin-top: 1rem;
}

.schema-table-name {
  margin: 0.8rem 0 0.4rem;
  font-size: 0.85rem;
  color: var(--text-muted);
}

.schema-table-name:first-child {
  margin-top: 0;
}

.table-scroll {
  overflow-x: auto;
  max-height: 280px;
  overflow-y: auto;
}

table.data-table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.86rem;
}

table.data-table th,
table.data-table td {
  border: 1px solid var(--border);
  padding: 0.4rem 0.6rem;
  text-align: left;
  white-space: nowrap;
}

table.data-table th {
  background: #f0f0f8;
  position: sticky;
  top: 0;
}

table.data-table tbody tr:nth-child(even) {
  background: #fafafe;
}

.placeholder {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin: 0;
}

/* Question list */

.question-list {
  list-style: none;
  margin: 0;
  padding: 0;
  max-height: 220px;
  overflow-y: auto;
}

.question-list li {
  cursor: pointer;
  padding: 0.5rem 0.6rem;
  border-radius: 6px;
  margin-bottom: 0.25rem;
  font-size: 0.9rem;
  border: 1px solid transparent;
}

.question-list li:hover {
  background: #f2f2fa;
}

.question-list li.active {
  background: #eceafc;
  color: var(--accent-dark);
  border-color: var(--accent);
  font-weight: 600;
}

.question-list li.sandbox-item {
  border-top: 1px dashed var(--border);
  margin-top: 0.4rem;
  padding-top: 0.6rem;
  font-style: italic;
  color: var(--text-muted);
}

.question-list li.sandbox-item.active {
  color: var(--accent-dark);
  font-style: normal;
}

.solution-box {
  margin-top: 0.8rem;
  padding: 0.6rem 0.7rem;
  background: var(--code-bg);
  color: var(--code-text);
  border-radius: 6px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.85rem;
  white-space: pre-wrap;
}

.solution-box[hidden] {
  display: none;
}

/* Editor */

.sql-input {
  width: 100%;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.92rem;
  background: var(--code-bg);
  color: var(--code-text);
  border: none;
  border-radius: 8px;
  padding: 0.8rem;
  resize: vertical;
}

.sql-input:focus {
  outline: 2px solid var(--accent);
}

.editor-actions {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-top: 0.7rem;
}

.run-btn,
.solution-btn {
  border: none;
  padding: 0.5rem 1.1rem;
  border-radius: 6px;
  font-size: 0.9rem;
  cursor: pointer;
  transition: background 0.15s ease;
}

.run-btn {
  background: var(--accent);
  color: #fff;
}

.run-btn:hover {
  background: var(--accent-dark);
}

.solution-btn {
  background: transparent;
  color: var(--text-muted);
  border: 1px solid var(--border);
}

.solution-btn:hover {
  color: var(--text);
  border-color: var(--text-muted);
}

.solution-btn[hidden] {
  display: none;
}

.status {
  font-size: 0.85rem;
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
}

.status.error {
  color: var(--error);
  background: var(--error-bg);
}

.status.success {
  color: var(--success);
  background: var(--success-bg);
}

/* Homework tab */

.homework-toolbar {
  display: flex;
  justify-content: flex-end;
  margin-bottom: 0.8rem;
}

.schema-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.6rem;
}

.schema-header .panel-title {
  margin: 0;
}

.add-row-btn {
  border: none;
  background: var(--accent);
  color: #fff;
  padding: 0.4rem 0.9rem;
  border-radius: 6px;
  font-size: 0.85rem;
  cursor: pointer;
}

.add-row-btn:hover {
  background: var(--accent-dark);
}

.modal-overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.4);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
}

.modal-overlay[hidden] {
  display: none;
}

.modal-box {
  background: var(--panel-bg);
  border-radius: 10px;
  padding: 1.2rem 1.4rem;
  width: min(90vw, 360px);
  box-shadow: 0 10px 40px rgba(0, 0, 0, 0.25);
}

.modal-box h3 {
  margin-top: 0;
}

.modal-field {
  display: flex;
  flex-direction: column;
  gap: 0.25rem;
  margin-bottom: 0.7rem;
  font-size: 0.85rem;
  color: var(--text-muted);
}

.modal-field input {
  font-size: 0.95rem;
  padding: 0.45rem 0.6rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  color: var(--text);
}

.modal-actions {
  display: flex;
  justify-content: flex-end;
  gap: 0.6rem;
  margin-top: 0.4rem;
}

/* Quiz tab */

.quiz-grid {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr;
  gap: 1rem;
}

@media (max-width: 760px) {
  .quiz-grid {
    grid-template-columns: 1fr;
  }
}

.quiz-prompt {
  margin-bottom: 0.8rem;
}

.quiz-prompt p:first-child {
  margin-top: 0;
}

.quiz-options {
  list-style: none;
  margin: 0 0 0.8rem;
  padding: 0;
}

.quiz-options li {
  cursor: pointer;
  padding: 0.6rem 0.8rem;
  border-radius: 6px;
  margin-bottom: 0.4rem;
  border: 1px solid var(--border);
}

.quiz-options li:hover {
  background: #f2f2fa;
}

.quiz-options li.selected {
  border-color: var(--accent);
  background: #eceafc;
}

.quiz-options li.correct {
  border-color: var(--success);
  background: var(--success-bg);
  color: var(--success);
  font-weight: 600;
}

.quiz-options li.incorrect {
  border-color: var(--error);
  background: var(--error-bg);
  color: var(--error);
}