/* A compact book-margin navigation rail; page height belongs to the content. */
:root { --sidebar-width: 76px; --page-sidebar-space: 76px; }
/* Center the book in the space remaining beside either rail width. */
body { padding-left: var(--page-sidebar-space); }
body.is-sidebar-expanded { --sidebar-width: 228px; --page-sidebar-space: 228px; }
.site-main { padding-top: 20px; }
.site-main:focus { outline: none; }
.site-sidebar {
    position: fixed;
    inset: 0 auto 0 0;
    z-index: 95;
    width: var(--sidebar-width);
    height: 100dvh;
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 12px 8px;
    background: var(--color-surface);
    border-right: 1px solid var(--color-border);
}
.sidebar-brand { flex: 0 0 52px; margin-bottom: 12px; }
.sidebar-brand img { display: block; width: 40px; height: 40px; }
.sidebar-nav {
    flex: 1;
    min-height: 0;
    width: 100%;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    gap: 16px;
}
.sidebar-pages, .sidebar-utilities { display: flex; flex-direction: column; align-items: center; gap: 4px; }
.sidebar-utilities { padding-top: 10px; border-top: 1px solid var(--color-border); }
.sidebar-link {
    --sidebar-icon-blue: var(--palette-navigation-blue);
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 54px;
    height: clamp(40px, 6.1dvh, 54px);
    flex-shrink: 0;
    border: 0;
    border-radius: 10px;
    background: transparent;
    color: var(--color-heading);
    cursor: pointer;
    text-decoration: none;
    transition: background-color .15s ease;
}
.sidebar-link:hover, .sidebar-link:focus-visible, .sidebar-account-menu[open] > summary {
    background: var(--color-surface-hover);
    text-decoration: none;
}
.sidebar-link:focus-visible { outline: 2px solid var(--color-link); outline-offset: 2px; }
.sidebar-link.is-active {
    --sidebar-icon-blue: var(--palette-primary);
    background: var(--palette-primary-soft);
}
.sidebar-link.is-active::before {
    content: "";
    position: absolute;
    left: -8px;
    top: 25%;
    bottom: 25%;
    width: 3px;
    border-radius: 0 3px 3px 0;
    background: var(--color-link);
}
.sidebar-icon { display: block; width: 44px; height: 44px; overflow: visible; pointer-events: none; }
.sidebar-label { display: none; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: 13px; font-weight: 500; }
.is-sidebar-expanded .sidebar-pages,
.is-sidebar-expanded .sidebar-utilities { align-items: stretch; }
.is-sidebar-expanded .sidebar-link { width: 100%; justify-content: flex-start; gap: 10px; padding-inline: 5px; }
.is-sidebar-expanded .sidebar-icon { flex: 0 0 40px; width: 40px; height: 40px; }
.is-sidebar-expanded .sidebar-label { display: block; }
.is-sidebar-expanded .sidebar-brand { width: 100%; }
.is-sidebar-expanded .sidebar-brand .sidebar-label { font-size: 16px; font-weight: 600; }
.is-sidebar-expanded .sidebar-link[data-tooltip]::after { content: none; }
.sidebar-link[data-tooltip]::after {
    content: attr(data-tooltip);
    position: absolute;
    left: calc(100% + 14px);
    top: 50%;
    transform: translateY(-50%);
    z-index: 1000000;
    width: max-content;
    max-width: min(340px, calc(100vw - 100px));
    padding: 8px 10px;
    border: var(--tooltip-border);
    border-radius: var(--tooltip-radius);
    background: var(--tooltip-background);
    color: var(--tooltip-color);
    box-shadow: var(--tooltip-shadow);
    font-size: .78rem;
    font-weight: 600;
    line-height: 1.35;
    text-align: center;
    white-space: pre-line;
    opacity: 0;
    visibility: hidden;
    pointer-events: none;
    transition: opacity .12s ease;
}
.sidebar-link[data-tooltip]:hover::after, .sidebar-link[data-tooltip]:focus-visible::after { opacity: 1; visibility: visible; }
.sidebar-link[data-sidebar-tooltip-ready]::after { content: none; }
.sidebar-account-menu[open] > summary::after { opacity: 0; visibility: hidden; }
.sidebar-account-menu > summary { list-style: none; }
.sidebar-account-menu > summary::-webkit-details-marker { display: none; }
.sidebar-account-panel {
    position: fixed;
    bottom: 12px;
    left: calc(var(--sidebar-width) + 8px);
    width: min(300px, calc(100vw - var(--sidebar-width) - 24px));
    max-height: calc(100dvh - 24px);
    overflow-y: auto;
    padding: 14px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: 12px;
    box-shadow: 0 12px 32px var(--color-shadow);
}
.sidebar-account-heading { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 8px; }
.sidebar-account-heading strong { font-size: 15px; font-weight: 600; overflow-wrap: anywhere; }
.sidebar-account-close {
    width: 28px;
    height: 28px;
    flex: 0 0 28px;
    padding: 0;
    display: grid;
    place-items: center;
    border: 0;
    border-radius: 50%;
    background: transparent;
    color: var(--color-heading);
    font: inherit;
    font-size: 22px;
    cursor: pointer;
}
.sidebar-account-close:hover { background: var(--color-surface-hover); box-shadow: var(--shadow-circular-control-hover); }
.sidebar-account-action {
    display: block;
    width: 100%;
    padding: 9px 10px;
    border: 0;
    border-radius: 6px;
    background: transparent;
    color: var(--color-link);
    text-align: left;
    text-decoration: none;
    font: inherit;
    font-size: 14px;
    cursor: pointer;
}
.sidebar-account-action:hover { background: var(--color-surface-hover); text-decoration: none; }
.sidebar-role-form { display: grid; gap: 8px; padding: 12px 0; margin: 6px 0; border-block: 1px solid var(--color-border); }
.sidebar-role-form label { font-size: 12px; color: var(--color-muted); }
.sidebar-role-form select { width: 100%; min-width: 0; padding: 8px; border: 1px solid var(--color-border); border-radius: 6px; background: var(--color-surface); color: var(--color-text); font: inherit; }
.sidebar-role-form .button { min-height: 34px; padding: 6px 10px; font-size: 13px; }
.site-skip-link { position: fixed; top: 8px; left: calc(var(--sidebar-width) + 12px); z-index: 1000001; padding: 10px 16px; border-radius: 6px; background: var(--color-surface); color: var(--color-link); transform: translateY(-150%); }
.site-skip-link:focus { transform: translateY(0); }
body.is-lesson-zen { padding-left: 0; --page-sidebar-space: 0px; }
body.is-lesson-zen .site-sidebar, body.is-lesson-zen .site-skip-link, body.is-lesson-zen .sidebar-tooltip { display: none !important; }
@media (max-height: 580px) {
    .site-sidebar { padding-block: 8px; }
    .sidebar-brand { flex-basis: 40px; margin-bottom: 6px; }
    .sidebar-brand img { width: 32px; height: 32px; }
    .sidebar-pages, .sidebar-utilities { gap: 1px; }
    .sidebar-nav { gap: 8px; }
    .sidebar-utilities { padding-top: 4px; }
    .sidebar-icon { width: 38px; height: 38px; }
}
@media (max-height: 430px) { .sidebar-pages { overflow-y: auto; overflow-x: hidden; flex: 1; } }
/* Retain the existing mobile-unavailable screen rather than overlap it. */
@media (max-width: 760px), (max-width: 900px) and (pointer: coarse) {
    body { padding-left: 0; --page-sidebar-space: 0px; }
    .site-sidebar, .site-skip-link, .sidebar-tooltip { display: none; }
}