How to Configure Strict CSS Corner-Shape (Superellipses) in Google Chrome

Modern user interface design—prominently popularized by modern mobile operating systems and high-end automotive displays—heavily utilizes “squircles” and superelliptical curves rather than standard circular rounded corners. Standard border-radius renders circular arcs that meet straight edges abruptly, producing subtle visual inflection points where the curvature suddenly drops to zero. The emerging CSS corner-shape property allows web authors to declare superellipses, bevels, and continuous curvature directly in stylesheet definitions. This tutorial demonstrates how to configure superelliptical corners and audit curvature in Google Chrome.

The Geometry of Superelliptical Squircles

A superellipse is defined mathematically by the Lamé curve equation |x/a|^n + |y/b|^n = 1. When n = 2, the formula yields a standard circle or ellipse. As the exponent increases (commonly n = 4 or n = 5), corners smoothly transition into adjacent straight edges with continuous mathematical curvature (G2 curvature continuity). The CSS corner-shape: squircle (or corner-shape: superellipse) instructs the browser rendering engine to interpolate corner radii using higher-order polynomial curves.

Authoring Continuous Curvature Buttons and App Icons

Implement the property across cards, avatar badges, and interactive controls:

.app-icon {
  width: 96px;
  height: 96px;
  background: linear-gradient(135deg, #6366f1, #a855f7);
  
  /* Traditional radius fallback */
  border-radius: 24px;
  
  /* Modern continuous curvature */
  corner-shape: squircle;
  
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 10px 25px -5px rgba(99, 102, 241, 0.4);
}

.modal-dialog {
  background-color: #ffffff;
  border-radius: 32px;
  corner-shape: squircle;
  padding: 2.5rem;
  max-width: 520px;
}

Enabling Experimental CSS Features in Google Chrome

Because CSS Borders and Backgrounds Module Level 4 specifications are rolling out across Chromium updates:

1. Open Google Chrome and navigate to chrome://flags.
2. Search for Experimental Web Platform features.
3. Toggle the selection to Enabled and relaunch Chrome.
4. Navigate to your staging application to evaluate native superelliptical corner rendering.

Inspecting Curvature and Fallbacks in Chrome DevTools

1. Right-click your squircle element and select Inspect to open Chrome DevTools.
2. In the Elements panel, select the DOM element and locate the Styles pane.
3. Verify that corner-shape: squircle is active and not strikethrough.
4. In the Computed panel, observe that the rasterized border path displays continuous tangency into adjacent edges without sharp transitions.

Providing SVG Clip-Path Fallbacks for Universal Support

For production browsers where corner-shape is not yet supported, provide a mathematically identical fallback using an inline SVG superellipse clip path:

.app-icon {
  border-radius: 24px;
}

@supports (corner-shape: squircle) {
  .app-icon {
    corner-shape: squircle;
  }
}

@supports not (corner-shape: squircle) {
  .app-icon.strict-squircle {
    clip-path: url(#squircle-clip);
  }
}