Theming

How to change the way the library looks. There are two independent controls:

Color

A Theme is three colors. Every other color is derived from them, so no token can drift out of step with the rest.

use limn::{Color, Theme};

let theme = Theme {
    background: Color::rgb(255, 255, 255),
    foreground: Color::rgb(24, 26, 31),
    accent: Color::rgb(9, 105, 218),
};
let palette = theme.palette();

Theme::DARK is the built-in dark theme.

Pass the palette to components and use the theme’s own colors for the page:

Element::panel(Button::new("save", "Save", palette).render())
    .background(theme.background)

What a theme derives

The palette

ComponentPalette is the subset components need:

palette.link() is the ink for links: a blue chosen to read on that palette, dark or light.

Hover and selection are veils, not opaque fills, so the same feedback reads on any surface. To give one component different colors, pass it a modified copy:

let danger = ComponentPalette { text: red, ..palette };

A scheme of explicit roles

A Theme derives every color from three. A host with a finished design has the opposite need: it knows each value and wants them named once. A Scheme is that list of roles, built as a const:

No component takes a Scheme. It only produces the palettes they take:

on takes the role of that color, because a scheme never guesses a role from a value:

let chosen_row = scheme.on(Surface::Raised(scheme.selected), scheme.text);

scheme.step(color) moves each channel 8 toward the ink: lighter in a dark scheme, darker in a light one. Alpha is kept.

theme.scheme() gives a theme’s colors by role, and theme.scheme().palette() equals theme.palette(). A scheme holds no status, link, diff or syntax colors: those stay with the host.

Light and dark together

Because color is a value passed to each component, nothing stops two palettes from sharing a window: a dark sidebar beside a light document, for instance.

Shape and pace

Corner radii and durations are set once:

use limn::{set_tokens, Motion, Radius, Tokens};

set_tokens(Tokens {
    radius: Radius::SQUARE,
    motion: Motion::DEFAULT.scaled(0.5),
    ..Tokens::DEFAULT
});

They are global because the library paints tooltips, menus, scrollbars and focus rings itself, without being handed a palette. Tokens lists every value.

Fonts

The faces limn lays text out in are limn::fonts(), one set for the whole process; limn::set_fonts replaces them, and a backend draws glyphs from the same bytes. See TextLayout. The rest of this section is about the faces egui lays its own text out in, which limn’s components still use.

limn_egui::install_fonts(&ctx) gives egui limn’s own faces, the same bytes limn lays text out in and in the same order: Ubuntu Regular, Medium and Bold for the UI, Hack for code, then Noto Sans Math, Noto Sans Symbols 2 and, last, Noto Emoji. Call it once when the window is created, before the first frame: limn-egui no longer turns on eframe’s default_fonts, so without it egui has no faces at all. A host that turns default_fonts on itself carries egui’s own faces as well, unused once these are installed; leave it off to keep one copy of each font.

Noto Sans Math 3.000 covers mathematical alphabets, including names such as 𝖗𝖚𝖓𝖊 and 𝓡𝓤𝓝𝓔, for regular, italic, medium, bold and monospace text; missing mathematical glyphs use Noto’s own shapes and widths, including inside monospace text. attach_fonts measures the same fallback that paints.

The bundled font adds about 1 MiB and uses SIL OFL-1.1; its unchanged license, version, pinned source and hashes are in crates/limn/assets/fonts/NOTICE.md. This is additional mathematical coverage, not general Unicode shaping, CJK coverage or color emoji. No fonts are read from the host’s system or downloaded at runtime.

Noto Sans Symbols 2 v2.008 follows Math in every family for missing decorative symbols, including ✦, ✧, ❖ and ➜. The unmodified, unhinted OpenType face adds 404,576 bytes under OFL-1.1, with its release source, hashes and full license alongside the Math notices. The Text gallery uses synthetic labels to demonstrate the fallback. Neither this font nor those tests imply that every user-supplied name is covered. The proportional families put Hack after the symbols, supplying box drawing such as ├─│╭╰║ without another font asset. Missing glyphs keep their fallback face’s advance width.

Noto Emoji 3.002 is last in all five families, so it never takes a symbol a text face has, and draws every monochrome emoji, including 🙂, 🤣, 🦀 and 🫡; egui’s own emoji faces are no longer installed. It adds 1,982,596 bytes under OFL-1.1. The original variable font, full license and pinned source hashes are bundled alongside the other font notices. Previously covered text retains its face and metrics; new emoji use the fallback’s own advance width, including in monospace text. There is no runtime font download or new runtime dependency.

The 623-entry synthetic fixture in limn-egui/src/emoji_samples.txt covers all visible scalars from RUNE’s Unicode picker at the time of this change. Tests inspect actual installed charmaps in all five families and exercise egui’s lookup, layout metrics and composition of ❤️, ☀️, 🧑‍💻 and 🏴‍☠️. The fixture contains only Unicode strings, without application data or assets. It is a coverage snapshot, not a complete emoji standard.

Scalar coverage is distinct from sequence shaping. egui 0.36 chooses the face for a grapheme from its first character. When that character already exists in an earlier font, the appended font cannot supply a missing combined glyph. For example, the regional flag 🇦🇷 still paints two glyphs, and some keycaps and joined flags remain incomplete. The fallback does not provide color emoji, complete combined-sequence support or CJK coverage. The Text gallery shows both supported samples and those limits.

Language

The words the library says by itself, such as the hint of a close button, the default actions of an alert dialog or the names in the text context menu, are in one value. They are English unless the host sets them, once:

limn::set_labels(limn::Labels::SPANISH);

// Or a few of them, in any language:
limn::set_labels(limn::Labels {
    close: "Fermer",
    cancel: "Annuler",
    ..limn::Labels::ENGLISH
});

Labels::ENGLISH and Labels::SPANISH are complete. A component that takes a label of its own, such as AlertDialog::confirm_label, uses these only when it is given none. FindBar, Markdown and DiagramViewer take their own labels, in FindLabels, MarkdownLabels and close_title.

What cannot be themed yet

• The easing curve of transitions.
• Font sizes, which each component sets for itself, and font weight.
• Spacing inside components.
• The icon size, 16 px.

See also

• Tokens for the reference tables.
• Animation for what the durations apply to.