.activity-page {
    width: min(1250px, calc(100% - 36px));
    margin: 0 auto;
    padding: 32px 0 80px;
}

.back-link {
    display: inline-block;
    margin-bottom: 25px;
    color: #555;
    font-size: 14px;
    font-weight: 700;
}

.back-link:hover {
    color: #e60023;
}

.activity-layout {
    display: grid;
    grid-template-columns: minmax(0, 1.05fr) minmax(360px, .95fr);
    gap: 48px;
    align-items: start;
}

.activity-preview {
    position: sticky;
    top: 100px;
    overflow: hidden;
    min-height: 420px;
    border-radius: 22px;
    background: #f4f4f4;
    box-shadow: 0 5px 25px rgba(0,0,0,.08);
}

.activity-cover {
    display: block;
    width: 100%;
    max-height: 760px;
    object-fit: contain;
    background: #f4f4f4;
}

.activity-placeholder {
    min-height: 420px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 8px;
    color: #777;
    text-align: center;
}

.file-icon {
    font-size: 70px;
    margin-bottom: 5px;
}

.activity-placeholder strong {
    color: #333;
    font-size: 19px;
}

.activity-placeholder span {
    font-size: 13px;
}

.activity-info {
    padding: 8px 0;
}

.activity-tags {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    margin-bottom: 16px;
}

.activity-tags a,
.activity-tags span {
    padding: 7px 10px;
    border-radius: 9px;
    background: #f1f1f1;
    color: #555;
    font-size: 12px;
    font-weight: 800;
}

.activity-tags a:hover {
    background: #111;
    color: white;
}

.activity-info h1 {
    margin: 0 0 20px;
    font-size: clamp(32px, 4vw, 48px);
    line-height: 1.05;
    letter-spacing: -1.5px;
}

.description {
    color: #555;
    font-size: 16px;
    line-height: 1.7;
    white-space: normal;
}

.author-box {
    display: flex;
    align-items: center;
    gap: 12px;
    margin: 28px 0;
    padding: 15px 0;
    border-top: 1px solid #eee;
    border-bottom: 1px solid #eee;
}

.author-photo {
    width: 46px;
    height: 46px;
    border-radius: 50%;
    object-fit: cover;
}

.author-placeholder {
    display: grid;
    place-items: center;
    background: #111;
    color: white;
    font-weight: 900;
    font-size: 18px;
}

.author-box div:last-child {
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.author-box small {
    color: #888;
    font-size: 11px;
}

.author-box strong {
    font-size: 14px;
}

.stats {
    display: flex;
    flex-wrap: wrap;
    gap: 16px;
    margin: 18px 0;
    color: #777;
    font-size: 13px;
}

.action-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin: 24px 0;
}

.secondary-button,
.download-button {
    min-height: 46px;
    padding: 0 18px;
    border-radius: 24px;
    border: 1px solid #ddd;
    font-family: inherit;
    font-size: 14px;
    font-weight: 800;
}

.secondary-button {
    background: white;
    color: #999;
    cursor: not-allowed;
}

.download-button {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    background: #e60023;
    color: white;
    border-color: #e60023;
}

.download-button:hover {
    background: #c9001f;
}

.file-info {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 15px;
    border: 1px solid #e7e7e7;
    border-radius: 14px;
    background: #fafafa;
}

.file-type {
    font-size: 25px;
}

.file-info div {
    display: flex;
    flex-direction: column;
    gap: 4px;
    min-width: 0;
}

.file-info strong {
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    font-size: 13px;
}

.file-info small {
    color: #888;
    font-size: 11px;
}

.notice {
    display: flex;
    flex-direction: column;
    gap: 5px;
    margin-top: 18px;
    padding: 15px;
    border-radius: 14px;
    background: #f6f6f6;
    color: #555;
    font-size: 12px;
    line-height: 1.5;
}

.notice strong {
    color: #333;
}

@media (max-width: 850px) {
    .activity-layout {
        grid-template-columns: 1fr;
        gap: 28px;
    }

    .activity-preview {
        position: static;
        min-height: 280px;
    }

    .activity-placeholder {
        min-height: 280px;
    }
}

@media (max-width: 600px) {
    .activity-page {
        width: min(100% - 22px, 600px);
        padding-top: 22px;
    }

    .activity-info h1 {
        font-size: 34px;
    }

    .activity-preview {
        border-radius: 16px;
    }

    .action-buttons > * {
        flex: 1 1 140px;
    }
}