Passthrough rendering is the core of Canvas. The theme takes the markup in your Custom HTML block and prints it to the page without wrapping it in a container or layering its own styles on top.
The problem it solves
Most themes wrap your content in a max-width container and inject block CSS that overrides your own rules. You set a width or a background, and the theme quietly constrains or repaints it. You then spend your time fighting the cascade to win back control of your own markup.
What Canvas does instead
Canvas renders Custom HTML blocks at full width, with no container constraints and no injected block styles. What you paste is what ships. Your CSS competes only with what you wrote and with WordPress core, not with a wall of theme declarations you can’t see.
If you want a centered, narrower layout, you set that width yourself in your own markup. Canvas doesn’t assume it for you.
Most themes wrap this in a fixed content width. Canvas hands it straight to the page.
