.v4-understand-nav {
    display: flex;
    align-items: center;
    gap: 10px;
    width: calc(100% - 24px);
    margin: 4px 12px 10px;
    padding: 11px 12px;
    text-align: left;
    font: 600 13px var(--font-family-base);
    color: var(--color-gray-700);
    background: transparent;
    border: 1px solid var(--color-gray-200);
    border-radius: var(--v4-radius-sm);
    cursor: pointer;
}
.v4-understand-nav-icon { font-size: 20px; flex-shrink: 0; }
.v4-understand-nav[hidden],.v4-mob-tab[data-mob-tab="understand"][hidden] { display: none !important; }
.v4-understand-nav:hover,
.v4-understand-nav.active {
    color: var(--color-primary);
    background: var(--color-primary-subtle);
    border-color: var(--color-primary);
}
.understand-view { max-width: 940px; margin: 0 auto; padding: 36px 32px 72px; color: var(--color-gray-900); }
.understand-view h1 { margin: 0 0 8px; font-size: 30px; line-height: 1.2; }
.understand-intro { margin: 0 0 24px; color: var(--color-gray-600); line-height: 1.5; }
.understand-search { display: block; width: 100%; max-width: 560px; padding: 12px 14px; border: 1px solid var(--color-gray-300); border-radius: 10px; background: var(--surface-primary); color: var(--color-gray-900); font: inherit; }
.understand-heading { margin: 30px 0 14px; font-size: 16px; font-weight: 600; }
.understand-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 12px; }
.understand-topic { min-height: 92px; padding: 17px; text-align: left; background: var(--surface-primary); border: 1px solid var(--color-gray-200); border-radius: 12px; color: var(--color-gray-900); cursor: pointer; font: inherit; }
.understand-topic:hover { border-color: var(--color-primary); background: var(--color-primary-subtle); }
.understand-topic-title { display: block; margin-bottom: 9px; font-weight: 600; }
.understand-topic-hint { color: var(--color-gray-600); font-size: 13px; }
.understand-empty { max-width: 570px; padding: 24px; border: 1px solid var(--color-gray-200); border-radius: 12px; background: var(--surface-primary); line-height: 1.5; }
.understand-empty p { margin: 0 0 14px; }
.understand-empty button, .understand-back, .understand-discuss { font: inherit; cursor: pointer; }
.understand-empty button, .understand-discuss { padding: 10px 14px; border: 1px solid var(--color-primary); border-radius: 9px; background: var(--color-primary); color: var(--color-white); }
.understand-back { padding: 0; margin: 0 0 24px; border: 0; background: transparent; color: var(--color-primary); }
.understand-meta { color: var(--color-gray-600); font-size: 13px; margin: 0 0 22px; }
.understand-summary { max-width: 720px; line-height: 1.65; overflow-x: auto; }
.understand-summary h2, .understand-summary h3, .understand-summary h4 { margin: 22px 0 10px; line-height: 1.3; }
.understand-summary table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 14px; }
.understand-summary th, .understand-summary td { padding: 8px; border: 1px solid var(--color-gray-200); text-align: left; vertical-align: top; }
.understand-summary p { margin: 0 0 14px; }
.understand-summary ul, .understand-summary ol { padding-left: 24px; }
.understand-summary li { margin: 6px 0; }
.understand-summary a { color: var(--color-primary); }
.understand-sections { max-width: 720px; margin-top: 30px; }
.understand-sections h2 { margin: 0 0 14px; font-size: 20px; }
.understand-sections-note { margin: -4px 0 14px; color: var(--color-gray-600); font-size: 13px; }
.understand-sections-status { color: var(--color-gray-600); }
.understand-section { margin-bottom: 9px; border: 1px solid var(--color-gray-200); border-radius: 10px; background: var(--surface-primary); }
.understand-section summary { padding: 15px 17px; font-weight: 600; cursor: pointer; list-style-position: inside; }
.understand-section summary span { float: right; color: var(--color-gray-600); font-size: 13px; font-weight: 400; }
.understand-section[open] summary { border-bottom: 1px solid var(--color-gray-200); }
.understand-section ul { margin: 0; padding: 7px 20px 12px 39px; }
.understand-section li { padding: 7px 0; line-height: 1.4; }
.understand-section li a { color: var(--color-primary); }
.understand-section li small { display: block; margin-top: 2px; color: var(--color-gray-600); }
.understand-actions { display: flex; align-items: center; flex-wrap: wrap; gap: 14px; margin-top: 24px; }
.understand-actions a { color: var(--color-primary); }
.understand-disclaimer { max-width: 720px; margin-top: 28px; padding-top: 16px; border-top: 1px solid var(--color-gray-200); color: var(--color-gray-600); font-size: 13px; line-height: 1.5; }
@media (max-width: 720px) {
    .understand-view { padding: 24px 18px 88px; }
    .understand-view h1 { font-size: 26px; }
    .understand-grid { grid-template-columns: 1fr; }
    .v4-mob-tab { flex: 1; min-width: 0; padding-left: 3px; padding-right: 3px; }
}