:root {
    --bg: #0d0f14;
    --surface: #13161e;
    --surface2: #1a1e2a;
    --border: #252936;
    --accent: #f97316;
    --accent2: #38bdf8;
    --accent3: #a78bfa;
    --green: #34d399;
    --yellow: #fbbf24;
    --text: #e2e8f0;
    --muted: #64748b;
    --code-bg: #0a0c11;
  }

  * { margin: 0; padding: 0; box-sizing: border-box; }

  body {
    background: var(--bg);
    color: var(--text);
    font-family: 'Sora', sans-serif;
    font-size: 14px;
    line-height: 1.7;
  }

  /* HEADER */
  .header {
    background: linear-gradient(135deg, #0d0f14 0%, #161929 50%, #0d1117 100%);
    border-bottom: 1px solid var(--border);
    padding: 40px 24px 32px;
    text-align: center;
    position: relative;
    overflow: hidden;
  }
  .header::before {
    content: '';
    position: absolute;
    top: -60px; left: 50%;
    transform: translateX(-50%);
    width: 500px; height: 200px;
    background: radial-gradient(ellipse, rgba(249,115,22,0.12) 0%, transparent 70%);
  }
  .header h1 {
    font-size: 28px;
    font-weight: 700;
    letter-spacing: -0.5px;
    position: relative;
  }
  .header h1 span.java { color: var(--accent); }
  .header h1 span.spring { color: var(--green); }
  .header p {
    color: var(--muted);
    margin-top: 8px;
    font-size: 13px;
  }
  .badge-row {
    display: flex;
    gap: 10px;
    justify-content: center;
    margin-top: 16px;
    flex-wrap: wrap;
  }
  .badge {
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 11px;
    font-weight: 600;
    letter-spacing: 0.5px;
  }
  .badge.java { background: rgba(249,115,22,0.15); color: var(--accent); border: 1px solid rgba(249,115,22,0.3); }
  .badge.spring { background: rgba(52,211,153,0.12); color: var(--green); border: 1px solid rgba(52,211,153,0.3); }
  .badge.count { background: rgba(56,189,248,0.12); color: var(--accent2); border: 1px solid rgba(56,189,248,0.3); }

  /* LAYOUT */
  .container { max-width: 900px; margin: 0 auto; padding: 24px 16px 60px; }

  /* SEARCH */
  .search-wrap {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--bg);
    padding: 14px 0;
    border-bottom: 1px solid var(--border);
    margin-bottom: 28px;
  }
  .search-inner {
    display: flex;
    gap: 10px;
    align-items: center;
  }
  #searchBox {
    flex: 1;
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 10px 16px 10px 40px;
    color: var(--text);
    font-family: 'Sora', sans-serif;
    font-size: 13px;
    outline: none;
    transition: border-color 0.2s;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%2364748b' stroke-width='2'%3E%3Ccircle cx='11' cy='11' r='8'/%3E%3Cpath d='m21 21-4.35-4.35'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: 12px center;
  }
  #searchBox:focus { border-color: var(--accent); }
  #searchBox::placeholder { color: var(--muted); }

  .filter-tabs {
    display: flex;
    gap: 6px;
    flex-wrap: wrap;
    margin-top: 10px;
  }
  .filter-tab {
    padding: 5px 14px;
    border-radius: 20px;
    font-size: 11px;
    font-weight: 600;
    cursor: pointer;
    border: 1px solid var(--border);
    background: var(--surface);
    color: var(--muted);
    transition: all 0.15s;
    letter-spacing: 0.3px;
  }
  .filter-tab:hover { color: var(--text); border-color: var(--muted); }
  .filter-tab.active { background: var(--accent); color: #fff; border-color: var(--accent); }
  .filter-tab.active.spring-tab { background: var(--green); border-color: var(--green); color: #000; }

  /* SECTION */
  .section-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin: 32px 0 16px;
  }
  .section-icon {
    font-size: 20px;
  }
  .section-title {
    font-size: 16px;
    font-weight: 700;
    letter-spacing: -0.3px;
  }
  .section-title.java-color { color: var(--accent); }
  .section-title.spring-color { color: var(--green); }
  .section-count {
    background: var(--surface2);
    color: var(--muted);
    font-size: 11px;
    padding: 2px 8px;
    border-radius: 10px;
    font-family: 'JetBrains Mono', monospace;
  }
  .subsection-label {
    font-size: 11px;
    font-weight: 600;
    letter-spacing: 1px;
    text-transform: uppercase;
    color: var(--muted);
    margin: 24px 0 12px;
    display: flex;
    align-items: center;
    gap: 8px;
  }
  .subsection-label::after {
    content: '';
    flex: 1;
    height: 1px;
    background: var(--border);
  }

  /* Q&A CARD */
  .qa-card {
    background: var(--surface);
    border: 1px solid var(--border);
    border-radius: 10px;
    margin-bottom: 10px;
    overflow: hidden;
    transition: border-color 0.2s;
  }
  .qa-card:hover { border-color: #353a4d; }
  .qa-card.hidden { display: none; }

  .qa-question {
    display: flex;
    align-items: flex-start;
    gap: 12px;
    padding: 14px 16px;
    cursor: pointer;
    user-select: none;
  }
  .qa-num {
    font-family: 'JetBrains Mono', monospace;
    font-size: 11px;
    color: var(--muted);
    min-width: 28px;
    margin-top: 1px;
    font-weight: 600;
  }
  .qa-q-text {
    flex: 1;
    font-weight: 600;
    font-size: 13.5px;
    color: var(--text);
    line-height: 1.5;
  }
  .qa-toggle {
    color: var(--muted);
    font-size: 16px;
    transition: transform 0.2s;
    min-width: 20px;
    text-align: center;
    margin-top: 1px;
  }
  .qa-card.open .qa-toggle { transform: rotate(180deg); color: var(--accent); }
  .qa-card.open .qa-question { border-bottom: 1px solid var(--border); }

  .qa-answer {
    display: none;
    padding: 16px 16px 16px 56px;
    color: #c4cdd8;
    font-size: 13px;
    line-height: 1.8;
  }
  .qa-card.open .qa-answer { display: block; }

  /* Answer styling */
  .qa-answer p { margin-bottom: 10px; }
  .qa-answer p:last-child { margin-bottom: 0; }
  .qa-answer strong { color: var(--accent2); font-weight: 600; }
  .qa-answer .highlight { color: var(--accent); font-weight: 600; }
  .qa-answer .green { color: var(--green); font-weight: 600; }
  .qa-answer .purple { color: var(--accent3); font-weight: 600; }
  .qa-answer .warn { color: var(--yellow); font-weight: 600; }

  .qa-answer ul {
    padding-left: 0;
    list-style: none;
    margin: 8px 0;
  }
  .qa-answer ul li {
    padding: 3px 0 3px 16px;
    position: relative;
  }
  .qa-answer ul li::before {
    content: '▸';
    position: absolute;
    left: 0;
    color: var(--muted);
    font-size: 10px;
    top: 5px;
  }

  .qa-answer .compare-table {
    width: 100%;
    border-collapse: collapse;
    margin: 10px 0;
    font-size: 12px;
  }
  .qa-answer .compare-table th {
    background: var(--surface2);
    padding: 7px 12px;
    text-align: left;
    font-weight: 600;
    color: var(--accent2);
    border: 1px solid var(--border);
  }
  .qa-answer .compare-table td {
    padding: 7px 12px;
    border: 1px solid var(--border);
    vertical-align: top;
    color: #c4cdd8;
  }
  .qa-answer .compare-table tr:nth-child(even) td { background: rgba(255,255,255,0.02); }

  code, .qa-answer code {
    font-family: 'JetBrains Mono', monospace;
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 4px;
    padding: 1px 6px;
    font-size: 12px;
    color: var(--accent);
  }

  .code-block {
    background: var(--code-bg);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 14px 16px;
    margin: 10px 0;
    font-family: 'JetBrains Mono', monospace;
    font-size: 12px;
    line-height: 1.7;
    overflow-x: auto;
    white-space: pre;
    color: #c4cdd8;
  }
  .code-block .kw { color: #c792ea; }
  .code-block .cl { color: #82aaff; }
  .code-block .fn { color: #82aaff; }
  .code-block .st { color: #c3e88d; }
  .code-block .cm { color: #546e7a; font-style: italic; }
  .code-block .an { color: #ffcb6b; }
  .code-block .num { color: #f78c6c; }
  .code-block .kw2 { color: var(--accent); }

  .tip-box {
    background: rgba(52,211,153,0.07);
    border-left: 3px solid var(--green);
    border-radius: 0 6px 6px 0;
    padding: 10px 14px;
    margin: 10px 0;
    font-size: 12.5px;
    color: #a7f3d0;
  }
  .warn-box {
    background: rgba(251,191,36,0.07);
    border-left: 3px solid var(--yellow);
    border-radius: 0 6px 6px 0;
    padding: 10px 14px;
    margin: 10px 0;
    font-size: 12.5px;
    color: #fde68a;
  }

  .tag { display: inline-block; padding: 2px 8px; border-radius: 4px; font-size: 11px; font-weight: 600; margin-right: 4px; font-family: 'JetBrains Mono', monospace; }
  .tag.java { background: rgba(249,115,22,0.15); color: var(--accent); }
  .tag.spring { background: rgba(52,211,153,0.12); color: var(--green); }

  #noResult {
    text-align: center;
    padding: 60px 20px;
    color: var(--muted);
    display: none;
  }
  #noResult .icon { font-size: 40px; margin-bottom: 12px; }

  /* scrollbar */
  ::-webkit-scrollbar { width: 6px; height: 6px; }
  ::-webkit-scrollbar-track { background: var(--bg); }
  ::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }
  ::-webkit-scrollbar-thumb:hover { background: var(--muted); }

  @media (max-width: 600px) {
    .header h1 { font-size: 20px; }
    .qa-answer { padding-left: 16px; }
    .compare-table { font-size: 11px; }
    .code-block { font-size: 11px; }
  }

  /* LEVEL BADGES */
  .level-badge {
    display: inline-flex;
    align-items: center;
    gap: 4px;
    padding: 2px 9px;
    border-radius: 20px;
    font-size: 10px;
    font-weight: 700;
    letter-spacing: 0.6px;
    text-transform: uppercase;
    white-space: nowrap;
    font-family: 'JetBrains Mono', monospace;
  }
  .level-badge.intern  { background: rgba(100,116,139,0.18); color: #94a3b8; border: 1px solid rgba(100,116,139,0.35); }
  .level-badge.junior  { background: rgba(52,211,153,0.13);  color: #34d399; border: 1px solid rgba(52,211,153,0.32); }
  .level-badge.middle  { background: rgba(56,189,248,0.13);  color: #38bdf8; border: 1px solid rgba(56,189,248,0.32); }
  .level-badge.senior  { background: rgba(249,115,22,0.15);  color: #f97316; border: 1px solid rgba(249,115,22,0.35); }
  .level-badge.expert  { background: rgba(167,139,250,0.15); color: #a78bfa; border: 1px solid rgba(167,139,250,0.35); }

  /* Level filter active states */
  .filter-tab.lv-intern.active  { background:#475569; border-color:#475569; color:#fff; }
  .filter-tab.lv-junior.active  { background:var(--green); border-color:var(--green); color:#000; }
  .filter-tab.lv-middle.active  { background:var(--accent2); border-color:var(--accent2); color:#000; }
  .filter-tab.lv-senior.active  { background:var(--accent); border-color:var(--accent); color:#fff; }
  .filter-tab.lv-expert.active  { background:var(--accent3); border-color:var(--accent3); color:#fff; }