The window opens but is completely invisible

A transparent window may have no visible border

If a window is recorded as open but has no background, check transparency first. Transparent backgrounds with unrendered content can look like no window at all, unlike an open call that never ran.

Rule out missing page content

1. Check whether content remains visibility:hidden, display:none, or fully transparent.
2. Check initialization errors that may prevent the reveal step.
3. Use an ordinary browser only for layout and static resources. It has no Blender bridge and cannot verify real data operations.
4. If transparency is unnecessary, the author can explicitly use an opaque declaration for diagnosis. This does not require changing system transparency settings.

For resource and script issues, see Blank-page troubleshooting. Explicit Python transparency takes precedence; changing only HTML does not prove a switch.

Check the corresponding editor region

Web windows belong to Blender editor regions, not arbitrary desktop floating windows. After layout or monitor changes or dragging, inspect the relevant region. Default placement or shift-enabled policies make minimal vertical corrections to keep the recovery/header area reachable, not necessarily recenter the whole window.

If reachable, drag the header back into view. With no content at all, investigate rendering rather than assuming position. Authors can reproduce with centered placement and reasonable dimensions. Transparency changes may require closing and reopening.

Verify visible content and working controls

• Real content appears in the originally affected editor.
• Transparent exterior and control regions behave as intended.
• The window remains visible after closing and reopening without accidental layout adjustments.

If content works in a browser but remains invisible in Blender, provide window state and original runtime errors for rendering diagnosis. Do not delete shared runtime components yourself.