Make preview overlay's inset configurable via CSS variable#95
Merged
cyanzhong merged 2 commits intoMarkEdit-app:mainfrom Apr 29, 2026
Merged
Make preview overlay's inset configurable via CSS variable#95cyanzhong merged 2 commits intoMarkEdit-app:mainfrom
cyanzhong merged 2 commits intoMarkEdit-app:mainfrom
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In preview-only mode, the preview pane uses position:absolute + inset:0, which is sized against the viewport regardless of any padding on body. That makes it impossible for a third-party plugin (e.g. a left-edge sidebar) to coexist with preview mode without overriding this rule via class-name targeting. Replace inset:0 with explicit top/right/bottom values plus left: var(--markedit-content-inset-left, 0). The fallback keeps existing behaviour identical when no plugin sets the variable. Plugins that occupy a horizontal slice on the left can now declare their offset via the CSS variable and compose cleanly with preview overlay mode without reaching into preview's class names.
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Thank you for your contribution. The idea makes sense to me. |
cyanzhong
reviewed
Apr 29, 2026
| top: 0; | ||
| right: 0; | ||
| bottom: 0; | ||
| left: var(--markedit-content-inset-left, 0); |
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@gpolitis Instead of only left, what about make inset a variable?
Do you think if it will be more useful or too much?
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Good call, agreed. Pushed 5beca15 switching to a single --markedit-content-inset variable. Plugins set the shorthand (e.g. --markedit-content-inset: 0 0 0 268px;), and calc() / nested var() work inside it.
Per review feedback: cover all four edges with one shorthand-valued custom property instead of a per-side variable for left only. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
cyanzhong
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Why
Third-party plugins that occupy a slice on the left edge of the viewport (e.g. a TOC sidebar) can't currently coexist with preview-only mode:
.markdown-body.overlayusesposition: absolute; inset: 0against the viewport, ignoring anypadding-inline-startonbody. The only workaround is!importantoverrides targeting preview's class names, which is fragile.Concrete example — my outline plugin currently ships with this compatibility shim:
https://github.com/gpolitis/MarkEdit-outline/blob/2cbbea0bb99de604a5a1cf73862155bcb95e8ee3/markedit-outline.js#L164-L170
The shim works but couples the two plugins via class-name targeting, which silently breaks if either side renames a class.
What
Replace
inset: 0with explicit per-side values, readingleftfrom a CSS custom property with a0fallback:A plugin that claims a left slice declares the variable on
bodywhen active:CSS custom properties cascade through the DOM, so preview's overlay pane picks it up automatically.
Backward compatibility
When no plugin sets the variable,
0is used and the layout is byte-identical to today. No other selectors changed.Scope
Scoped to
leftonly since that's the only side affected today. If future plugins need other edges, mirror variables fortop/right/bottomare a natural addition — leaving that for when there's a concrete use case.