Same background colors for Custom Containers and Code Blocks in dark theme

[Summer-Shen]

When viewing the docs in dark theme, both Custom Containers and Code Blocks have the same background color of var(--vt-c-bg-soft). When Code Blocks are nested in Custom Containers (see example), the colors can be confusing.

I also checked VitePress -- it seems that the issue is with the custom theme of the vuejs/docs repo.