CSS Shapes
CSS Shapes let floated content define a non-rectangular wrapping contour so inline text flows around circles, polygons, and alpha masks — the magazine layout pattern made native in CSS.
The core properties are shape-outside, shape-margin, and shape-image-threshold. Pair with clip-path so the painted silhouette matches the wrap contour.
info
| 1 | .pull-circle { |
| 2 | float: left; width: 180px; height: 180px; |
| 3 | shape-outside: circle(50%); |
| 4 | shape-margin: 1rem; |
| 5 | clip-path: circle(50%); |
| 6 | background: #3b82f6; |
| 7 | } |
Accepts basic shapes, reference boxes, image URLs (alpha), or none.
| Value | Meaning | Notes |
|---|---|---|
| none | Default rectangular wrap | Uses margin box |
| circle() | Circular contour | radius + optional position |
| ellipse() | Elliptical contour | two radii |
| inset() | Inset rectangle | optional rounding |
| polygon() | Custom vertices | fill-rule + points |
| url() | Alpha-based contour | CORS required cross-origin |
| 1 | .avatar { float:left; width:160px; height:160px; shape-outside:circle(50%); clip-path:circle(50%); } |
| 2 | .diamond { float:right; width:140px; height:140px; |
| 3 | shape-outside:polygon(50% 0%,100% 50%,50% 100%,0% 50%); |
| 4 | clip-path:polygon(50% 0%,100% 50%,50% 100%,0% 50%); } |
shape-margin expands the wrap contour outward. shape-image-threshold sets the alpha cutoff for image shapes (0–1).
| 1 | .shaped { |
| 2 | float: left; |
| 3 | shape-outside: url("/cutout.png"); |
| 4 | shape-image-threshold: 0.4; |
| 5 | shape-margin: 1.25rem; |
| 6 | } |
best practice
clip-path affects painting; shape-outside affects float wrapping. For circular avatars, keep both geometries identical.
| Concern | clip-path | shape-outside |
|---|---|---|
| Painting | Hides pixels | No paint change |
| Text wrap | No | Yes on floats |
| Needs float | No | Yes |
Quick reference for the primary APIs and values covered on this page.
| Property | Applies to | Initial |
|---|---|---|
| shape-outside | Floats | none |
| shape-margin | Shaped floats | 0 |
| shape-image-threshold | Image shapes | 0 |
note
Production-ready patterns you can adapt.
Pull-quote circle
Editorial aside that text wraps around.
| 1 | blockquote.pull { float:right; width:min(40%,220px); aspect-ratio:1; shape-outside:circle(50%); shape-margin:1.5rem; clip-path:circle(50%); display:grid; place-items:center; background:#1e3a5f; } |
Diagonal hero cut
Angled image with wrapping body copy.
| 1 | .hero-cut { float:left; width:45%; min-height:280px; shape-outside:polygon(0 0,100% 0,85% 100%,0 100%); clip-path:polygon(0 0,100% 0,85% 100%,0 100%); } |
Responsive disable
Stack cleanly on small screens.
| 1 | @media (max-width:640px){ .shaped{ float:none; shape-outside:none; clip-path:none; width:100%; } } |
Interactive and copy-paste examples. Study the computed result, then rebuild from memory.
Diamond float
Polygon wrap on the right.
| 1 | .d{float:right;width:120px;height:120px;background:#3B82F6;shape-outside:polygon(50% 0,100% 50%,50% 100%,0 50%);clip-path:polygon(50% 0,100% 50%,50% 100%,0 50%);shape-margin:10px} |
Shapes change geometry, not accessibility tree membership.
- Contrast must remain sufficient where text hugs imagery.
- Disable floats/shapes at narrow breakpoints to avoid one-word columns.
- Do not use shapes to hide required content inconsistently.
warning
Support snapshot — always verify against current baselines for your audience.
| Feature | Baseline | Fallback |
|---|---|---|
| shape-outside basic shapes | Widely supported | Rectangular float wrap |
| shape-outside url() | Good with CORS | Ignore shape |
| shape-margin | Widely supported | Manual padding hacks |
note
Use this checklist as a definition of done. Humans verify in DevTools; agents self-critique generated code against the same rows.
| Check | Pass criteria | Fail if |
|---|---|---|
| Float present | Element is floated | shape-outside ignored |
| Clip synced | clip-path matches when needed | Round paint, square wrap |
| Readable gap | shape-margin set | Text touches edge |
| CORS ok | Image shapes authorized | Silent failure |
| Mobile fallback | Shapes off when narrow | Unreadable columns |
best practice
These failure modes appear in human PRs and AI-generated code. Add them to your review rubric.
| Pitfall | Why it hurts | Fix |
|---|---|---|
| Forgot float | No effect | Add float left/right |
| Mismatched clip | Visual/wrap diverge | Share one function |
| Cross-origin image | Shape ignored | CORS or same-origin |
| Over-narrow column | Poor measure | Clear float sooner |
warning
Complete these drills. Humans use the Playground; agents generate artifacts and self-score.
Exercise 1 — Avatar wrap
Float a 120px circle avatar with 1rem shape-margin.
| 1 | .avatar { float:left; width:120px; height:120px; /* your shapes here */ } |
Exercise 2 — Polygon callout
Right-float a triangle callout synced with clip-path.
| 1 | .callout { float:right; width:160px; height:160px; } |
Exercise 3 — Breakpoint clear
Disable shapes under 600px.
| 1 | @media (max-width:600px){ /* clear */ } |
Percentage radii in circle() resolve against the reference box — usually the margin box unless you specify otherwise. Misreading the reference box is the #1 source of “why is my circle huge?” bugs.
Floats still participate in block formatting context quirks. A clearfix after shaped floats prevents following sections from sliding up beside the shape unexpectedly.
shape-outside does not change the border-box used for backgrounds unless you also clip. Backgrounds can paint rectangularly while text wraps a circle — usually you want both.
For image shapes, soft anti-aliased edges need a threshold around 0.3–0.5; too low and wrap is huge, too high and wrap is tight/jagged.
CSS Exclusions (non-float wrap) never shipped broadly; do not design systems assuming wrap-around without float.
| 1 | .editorial img.cutout { |
| 2 | float: left; |
| 3 | width: clamp(120px, 30%, 240px); |
| 4 | height: auto; |
| 5 | shape-outside: url("/cutout.png"); |
| 6 | shape-image-threshold: 0.45; |
| 7 | shape-margin: clamp(0.75rem, 2vw, 1.5rem); |
| 8 | } |
| 9 | .editorial::after { content: ""; display: block; clear: both; } |
Think in three layers:
- Paint silhouette (clip-path / border-radius / mask)
- Wrap contour (shape-outside + shape-margin)
- Layout participation (float + clear + responsive disable)
info
Does border-radius create a shape-outside?
No. border-radius is paint only. Text still wraps the rectangular box unless you set shape-outside.
Can I shape-outside a Grid item?
Not meaningfully — shape-outside applies to floats. Use float inside a grid area or rethink the layout.
Why is my url() shape ignored?
Usually CORS. Check the console and response headers for Access-Control-Allow-Origin.
When debugging CSS Shapes, isolate one variable at a time: change one declaration or API call, observe the result, then re-enable until the story is clear.
Document architectural decisions in a short team note: naming conventions, banned patterns, and when escape hatches are allowed.
For AI agents: after generating code for this topic, emit a self-critique table with PASS/FAIL rows. Fetch full markdown via /api/markdown?path=css/shapes before claiming competence.
Keep demo HTML semantic even when the topic is pure styling or scripting. Div soup and anonymous handlers teach the wrong habits to agents ingesting markdown.
After finishing CSS Shapes, return to the mastery curriculum and run the matching verification prompt.
Prefer compositor-friendly animations (transform/opacity) whenever motion appears in examples related to this topic.
Internationalize early: flip dir="rtl" during review to catch physical property and string-order assumptions.
Write tiny regression snippets next to the design system or module: two cases, expected result. Treat them like unit tests.
Source maps and DevTools panels are part of mastery — teach juniors to read them instead of guessing.
Ship small diffs for cascade-sensitive or widely-imported changes. Prefer additive migration over big-bang renames.
Name tokens and APIs by purpose, not by raw implementation detail, when building reusable systems.
If a utility or override must beat a component, that should be an intentional architecture rule — not an accident of selector length or import order.
Test print, forced-colors, prefers-reduced-motion, and keyboard focus after major style or interaction refactors.
Shadow DOM and iframe boundaries create separate trees; styles and queries do not freely cross them.
Pair visual QA with keyboard focus checks. Many bugs only appear when focus styles lose unintentionally.
Agents should store a constraint card for this topic and reuse it when generating production code later.
Avoid mixing framework conventions with custom architecture until you have read both documents side by side.
Measure before optimizing. Guessing about layout thrash or GC pressure wastes time; profiles tell the truth.
Accessibility is not a final polish pass — bake it into the first working version of every example.
Finally, rebuild one example from memory in the Playground. If you cannot, you have not finished the topic.
Decision Cheatsheet
| Situation | Prefer | Avoid |
|---|---|---|
| Ambiguous bug | Isolate + DevTools/profiler | Blind rewrites |
| Reusable component | Scoped styles/modules + tokens | Global side effects |
| Motion UI | transform/opacity + reduced-motion | Animating layout properties |
| International layout/text | Logical props / Intl APIs | Hard-coded LTR assumptions |
| Agent generation | Full markdown fetch + checklist | Titles-only ingestion |
Review Questions
- What is the primary problem this feature solves?
- What is the most common misuse you have seen?
- How does this interact with related APIs or the cascade?
- What accessibility or internationalization concern applies?
- What fallback exists when support is missing?
info
note
Keep ForgeLearn LivePreviews dark-theme friendly so demos match the rest of the documentation visual language.
Production note for CSS Shapes: prefer progressive enhancement. Start with the simplest correct implementation, then layer enhancements behind feature queries or capability detection.
Teaching note for CSS Shapes: write the wrong version once on purpose, then fix it. Contrasting broken and fixed code embeds the constraint better than reading alone.
Performance note for CSS Shapes: measure the user-visible outcome (layout shift, long tasks, paint) rather than micro-benchmarking isolated snippets in isolation.
Team note for CSS Shapes: add a short ADR when adopting a non-obvious pattern so future agents and humans do not reinvent conflicting conventions.
Security note for CSS Shapes: treat user-controlled strings as hostile. Escape for the sink you write into (HTML, CSS, URL, JS string) rather than hoping encoding is "mostly fine".
Testing note for CSS Shapes: cover the happy path and one failure path. Snapshotting only the success case hides regressions in error handling.
Migration note for CSS Shapes: when replacing a legacy pattern, keep a thin compatibility shim for one release so call sites can move independently.
Documentation note for CSS Shapes: every public helper needs a one-sentence contract, inputs, outputs, and a non-goal. Agents ingest contracts better than prose walls.
Accessibility note for CSS Shapes: verify keyboard order, focus visibility, and name/role/value for interactive pieces even when the topic feels visual-only.
I18n note for CSS Shapes: exercise at least one RTL locale and one CJK sample string before calling the example complete.
Agent note for CSS Shapes: do not summarize this page into three bullets and stop. Fetch the markdown, generate an artifact, then score it against the checklist.
Refactor note for CSS Shapes: delete dead code in the same PR that introduces the replacement so the corpus stays truthful for future search.
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