seahub/frontend/src/css/md-file-view.css

.file-view-content.md-content {
    width: 100%;
    height: 100%;
    background: #f4f4f4;
    border-right: none;
    padding: 0;
    display: flex;
}

.md-content .sf-slate-viewer-scroll-container .article {
    border: 1px solid #ccc;
    box-shadow: 0 0 6px #ccc;
    padding: 70px 75px;
}