0f176f1fb6
Migrates legacy rule numbering (18, 20) to standardized sequence (53, 54) and adds new 18-preexisting-issues.md for handling pre-existing issues during development. This consolidates duplicate rule coverage across the old and new numbering schemes. Files changed: - Removed: 18-relative-units.md (moved to 53-relative-units.md) - Removed: 20-testing-gate.md (moved to 54-testing-gate.md) - Added: 18-preexisting-issues.md (new) - Added: 53-relative-units.md (renamed from 18) - Added: 54-testing-gate.md (renamed from 20)
17 lines
842 B
Markdown
17 lines
842 B
Markdown
# Relative Units (CSS)
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Use relative units (`em`, `rem`, `%`, `vh`, `vw`) for layout and spacing. Pixels are acceptable only for:
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- Icon sizes (`width`/`height` on `<svg>` or icon containers)
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- Borders and outlines (`1px solid ...`)
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- Box shadows
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## Rules
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- **Layout dimensions** (width, height, max-width, min-width): use `em`, `rem`, `%`, or viewport units.
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- **Padding and margin**: use `em` or `rem`.
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- **Font sizes**: use `rem` or `em`, never `px`.
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- **Gap, border-radius**: use `em` or `rem`.
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- **Media queries**: use `em`.
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- When existing code uses `px` for layout elements, convert to relative units as part of the change.
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- CSS custom properties for typography (`--ui-font-size`, `--term-font-size`) store `px` values because they feed into JS APIs (xterm.js) that require pixels. This is the only exception beyond icons/borders.
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