:root {
    --bg: #f5f6f8;
    --panel: #ffffff;
    --line: #d9dee5;
    --text: #1f2937;
    --muted: #6b7280;
    --accent: #111827;
}

*,
*::before,
*::after {
    box-sizing: border-box;
}

body {
    margin: 0;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    color: var(--text);
    background: var(--bg);
}

.app {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.app__header {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 14px 18px;
    border-bottom: 1px solid var(--line);
    background: var(--panel);
}

.app__title {
    margin: 0;
    font-size: 20px;
    font-weight: 700;
}

.burger {
    display: none;
    width: 40px;
    height: 40px;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: #fff;
    padding: 8px;
    cursor: pointer;
}

.burger span {
    display: block;
    width: 100%;
    height: 2px;
    margin: 4px 0;
    background: var(--accent);
}

.app__layout {
    flex: 1;
    display: grid;
    grid-template-columns: 320px 1fr;
    min-height: 0;
}

.toc {
    border-right: 1px solid var(--line);
    background: var(--panel);
    padding: 16px;
    overflow: auto;
}

.toc__title {
    margin: 0 0 12px;
    font-size: 16px;
}

.toc__list {
    list-style: none;
    margin: 0;
    padding: 0;
}

.toc__item + .toc__item {
    margin-top: 8px;
}

.toc__button {
    width: 100%;
    text-align: left;
    border: 1px solid var(--line);
    background: #fff;
    color: var(--text);
    border-radius: 8px;
    padding: 10px 12px;
    cursor: pointer;
}

.toc__button.is-active {
    border-color: var(--accent);
    background: #f3f4f6;
}

.toc__empty {
    margin: 14px 0 0;
    color: var(--muted);
}

.viewer {
    padding: 16px;
    min-width: 0;
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.viewer__placeholder {
    border: 2px dashed var(--line);
    border-radius: 12px;
    background: #fff;
    min-height: 360px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--muted);
    text-align: center;
    padding: 24px;
}

.viewer__toolbar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 16px;
    flex-wrap: wrap;
}

.viewer__title {
    margin: 0;
    font-size: 18px;
}

.viewer__download {
    color: #fff;
    background: var(--accent);
    border-radius: 8px;
    text-decoration: none;
    padding: 8px 12px;
}

.viewer__actions {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
}

.viewer__action-button {
    border: 1px solid var(--line);
    background: #fff;
    color: var(--text);
    border-radius: 8px;
    padding: 8px 12px;
    cursor: pointer;
}

.viewer__action-button:disabled {
    opacity: 0.45;
    cursor: not-allowed;
}

.viewer__page-indicator {
    font-size: 14px;
    color: var(--muted);
    min-width: 68px;
    text-align: center;
}

.viewer__container {
    border: 1px solid var(--line);
    border-radius: 12px;
    background: #fff;
    min-height: 70vh;
    overflow: hidden;
}

.pdf-fallback {
    width: 100%;
    height: 70vh;
}

.pdf-fallback__frame {
    width: 100%;
    height: 100%;
    border: 0;
}

.viewer__notice {
    margin: 16px;
    padding: 12px;
    border: 1px solid var(--line);
    border-radius: 10px;
    color: var(--muted);
}

.viewer__image-list {
    margin: 0;
    padding: 16px;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 12px;
    list-style: none;
}

.viewer__image-page {
    width: 100%;
    border: 1px solid var(--line);
    border-radius: 8px;
}

.flipbook-shell {
    width: 100%;
    min-height: 70vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: #eef2f7;
    padding: 12px;
}

.flipbook-stage {
    width: min(92vw, 1200px);
    height: min(78vh, 900px);
}

@media (max-width: 980px) {
    .burger {
        display: inline-block;
    }

    .app__layout {
        grid-template-columns: 1fr;
        position: relative;
    }

    .toc {
        position: fixed;
        top: 69px;
        left: 0;
        bottom: 0;
        width: min(86vw, 360px);
        transform: translateX(-100%);
        transition: transform 0.2s ease;
        z-index: 30;
    }

    .toc.toc--open {
        transform: translateX(0);
    }

    .viewer {
        padding: 12px;
    }

    .viewer__container {
        min-height: 60vh;
    }
}