Nested Container Frames嵌套容器框架

Create a container-in-container layout system using nested frames. Use an outer centered container with visible vertical boundary lines and corner markers. Inside, place inner containers inset from the edges, each with its own background and rounded frame. Technique: outer container defines global bounds, inner containers use padding to create inset spacing, layered frames (border + background) to separate levels, and consistent spacing between outer frame and inner blocks.

创建嵌套框架布局系统：外层居中容器带可见垂直边界线和角点标记，内部容器从边缘内缩，并拥有各自的背景和圆角框架。