Styling

<Button className="rounded-circular px-5">Rounded</Button>
<Button appearance="primary" className="min-w-40">Wider</Button>
<Badge className="tracking-wide uppercase">New</Badge>

cn() in src/lib/cn.ts is clsx + tailwind-merge, configured to know Yugen's scales. Without that, plain tailwind-merge treats text-body1 as a text color and drops it when it meets text-foreground-1, so the text falls back to the default size. The actual output of cn() on this page:

Spacing

Spacing uses Tailwind's numeric scale: p-3, gap-2, mt-6. The ten steps below match Fluent's spacing ramp, so moving from Fluent UI is a rename: spacingHorizontalM → px-3. Keep padding, margin and gap within these ten steps; element sizes (h-8, size-5, w-64) use the other numbers.

The old uppercase aliases (p-M, gap-SNudge) still work but are deprecated since 0.10 and will be removed in 1.0. Replace them using the right-hand column of the table.

Since the source lives in your project, the shadcn way is to edit the variants table in Button.tsx directly. To keep the original file untouched so updates stay easy, wrap the component and add variants with cva:

import { cva, type VariantProps } from "class-variance-authority";
import { Button, type ButtonProps } from "@/components/ui";
import { cn } from "@/lib/cn";

const pillVariants = cva("rounded-circular", {
  variants: {
    tone: {
      neutral: "",
      brand:
        "border-transparent bg-brand-background-2 text-brand-foreground-2 hover:bg-brand-background-2-hover active:bg-brand-background-2-pressed",
    },
  },
  defaultVariants: { tone: "neutral" },
});

type PillButtonProps = ButtonProps & VariantProps<typeof pillVariants>;

export function PillButton({ tone, className, ...props }: PillButtonProps) {
  return <Button className={cn(pillVariants({ tone }), className)} {...props} />;
}

<PillButton>Neutral</PillButton>
<PillButton tone="brand" icon={<Star20Regular />}>Starred</PillButton>

Components also export their variant functions so you can style other elements: buttonVariants, linkVariants, imageVariants, toggleButtonVariants. For example <a className={buttonVariants({ appearance: "primary" })}>, although <Button asChild> is usually shorter (see Slots).

<MenuTrigger asChild>
  <Button
    appearance="subtle"
    icon={<ChevronDown20Regular className="transition-transform duration-normal" />}
    iconPosition="after"
    className="data-[state=open]:bg-subtle-pressed data-[state=open]:text-foreground-1 data-[state=open]:[&_svg]:rotate-180"
  >
    Sort
  </Button>
</MenuTrigger>

{/* A medium Button sets [&_svg]:size-5, so a 16px icon needs the ! suffix (Tailwind v4) */}
<Button icon={<Star20Regular className="size-4!" />}>16px icon in a medium button</Button>

Use the ! suffix (Tailwind v4 syntax, placed at the end of the class) only when a parent component sets a more specific selector such as [&_svg]:size-5. Don't sprinkle ! to beat the component's own classes; your className already comes last in cn().

Example: a custom read-only field that still has the stroke-accessible bottom edge and the brand bar on focus (click it or Tab to it):

import { fieldControlClass } from "@/components/ui";
import { cn } from "@/lib/cn";

<div
  tabIndex={0}
  role="textbox"
  aria-readonly
  aria-label="Referral code"
  className={cn(fieldControlClass, "flex h-8 w-64 items-center px-2.5 font-mono text-body1")}
>
  YUGEN-2026-SAKURA
</div>

npx @yugen-ui/cli@latest css

It writes yugen-ui.css next to your main CSS file and replaces @import "yugen-ui/theme.css" with @import "./yugen-ui.css". yugen init sets this up for new projects.

/* src/yugen-ui.css, written by yugen css */
@import "yugen-ui/theme-core.css";
/* One line per component folder your code imports. */
@import "yugen-ui/sources/Button.css";
@import "yugen-ui/sources/DataGrid.css";
@import "yugen-ui/sources/Dialog.css";
@import "yugen-ui/sources/YugenProvider.css";

• CSS gzip, including the app's own classes, measured with scripts/measure-css.mjs.
• Run the command again after you import another component (in package mode yugen add does it), or put it in your predev / prebuild scripts. yugen css --check exits with 1 when the file is out of date, and yugen doctor warns about it. See the CLI page.
• Each file already includes the components that component uses inside (SplitButton.css has Menu and Button), so list only the components you import.
• The file is named after the component's folder: NavItem is in sources/Nav.css, toast in sources/Toast.css. The export → file table is in yugen-ui/sources/index.json. You can also write these lines by hand.
• A missing file leaves that component unstyled. import * as, export * and import("yugen-ui") can reach any component, so the generated file falls back to theme.css when it finds one.
• Without Tailwind: yugen css --precompile compiles the same list into plain CSS that replaces styles.css.
• Not needed when you copy component source (shadcn registry, @yugen-ui/cli add): Tailwind already scans the app's folders. styles.css (no Tailwind) always contains every component.

<div className="flex items-center gap-3">
  <Avatar name="Emma Collins" color="colorful" size={40} />
  <div className="min-w-0 flex-1">
    <p className="truncate text-body1 font-semibold text-foreground-1">Emma Collins</p>
    <p className="truncate text-caption1 text-foreground-3">Product designer · International Payments…</p>
  </div>
  <div className="flex shrink-0 items-center gap-1">
    <Button size="small">Message</Button>
    <Button size="small" appearance="subtle" icon={<MoreHorizontal20Regular />} aria-label="More actions" />
  </div>
</div>

• min-w-0 flex-1 on the text block: a flex item doesn't shrink below its content by default, so without min-w-0, truncate has no effect and the row overflows.
• shrink-0 on the avatar and the action group keeps their size when the text is long.
• gap-* instead of margins, which stays correct in RTL. CardHeader, ListItem, TableCellLayout and Persona already package this pattern.