Twenty Nineteen: fix Separator block's full-width size and placement

[irozum]

Fixes the Twenty Nineteen Separator block so that Full width alignment actually spans the full page width, for both the Default and Wide Line styles. Currently the block's own max-width/width rules ignore the alignfull alignment entirely, so choosing Full width has no visible effect on the frontend and the separator is barely visible in the block editor.

Frontend (sass/blocks/_blocks.scss): the Separator block's own max-width: 2.25em (Default) and the is-style-wide bounded max-width were never overridden when .alignfull was applied. Added &.alignfull:not(.is-style-dots) { max-width: none; } so a full-width Default or Wide Line separator now spans edge-to-edge, matching the rest of the theme's full-width block handling. The Dots style is intentionally excluded, since it already renders at a deliberately bounded width.

Editor (style-editor.scss): the editor styles only set an explicit width for the narrow Default style ($font__size-xl); nothing widened the separator when it carried the alignfull class, which is why it appeared barely visible in the editor. Added &.alignfull:not(.is-style-dots) { width: 100%; }, placed after the narrow-width rule so it takes precedence when both classes are present.

Note: the ticket's original 2022 patch also suggested adding a block-editor-iframe__body selector to fix a missing editor margin; that generic fix already landed separately (visible at style-editor.scss:39) and covers this case, so no further change was needed there.

Both compiled style.css and style-editor.css were updated by hand to match, since this environment's Node toolchain couldn't rebuild the theme's SCSS via node-sass (native build failure unrelated to this change); the added rules were hand-verified against the existing compiled output's formatting conventions.

Manual verification: activated Twenty Nineteen locally and tested all four combinations directly in the running site (frontend + block editor, via computed styles and screenshots):

• Default style + Full width → now spans full width (was capped at 2.25em)
• Wide Line style + Full width → now spans full width (was capped at the content max-width)
• Default style, no alignment → unchanged (still 2.25em), confirming no regression
• Dots style + Full width → unchanged (still bounded by content max-width), confirming it was correctly left out of scope

Trac ticket: https://core.trac.wordpress.org/ticket/59203

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Sonnet 5
Used for: Implementation and manual browser verification. Reviewed by Igor Rozum.

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