/* 长器材封面完整显示；图片仍使用独立WebP映射与现有加载策略。 */
.thumbnail-diagram.diagram-roller-coaster-energy-3d,
.thumbnail-diagram.diagram-work-energy-theorem-3d,
.thumbnail-diagram.diagram-work-angle-projection-3d,
.thumbnail-diagram.diagram-gravity-work-potential-3d,
.thumbnail-diagram.diagram-spring-work-energy-3d{background-size:contain;background-position:center;background-color:#182831;}