自定义主题

fn mountUI(cx: *ui.Cx, scope: *ui.Scope) anyerror!*ui.Node {
    // Cx starts on ui.theme.dark. Pick the theme before building any node,
    // so every component reads the right tokens when it mounts.
    cx.setTheme(&ui.theme.light);

    const root = try ui.boxStyled(cx, S.root, .{});
    // …
    return root;
}

pub const ThemeTokens = struct {
    name: []const u8 = "unnamed",
    scheme: ColorScheme = .light,      // .light / .dark — the one flag for "is this dark?"
    color: ColorTokens,                // 54 colors, no defaults: you must provide all of them
    space: SpaceScale = .{},           // _0 … _12  (0 … 48 px, 4 px grid)
    radius: RadiusScale = .{},         // none sm md lg xl full
    font_size: FontSizeScale = .{},    // xxs … xxxl (9 … 24)
    border_width: BorderWidthScale = .{},
    size: SizeTokens = .{},            // checkbox, switch, badge, dot, close button
    control: ControlScale = .{},       // xs / sm / md / lg metrics for every control
    duration: DurationTokens = .{},    // fast / normal / slow (seconds)
    shadow: ShadowTokens = .{},        // sm / md / lg
};

// theme.zig — your app's themes. Container-level consts: they are
// evaluated at compile time and live for the whole program, which is
// what cx.setTheme(&brand) needs (it keeps the pointer).
const ui = @import("ui");

pub const brand: ui.ThemeTokens = blk: {
    var t = ui.theme.light; // copy a complete preset (every color is required)
    t.name = "brand";
    t.scheme = .light;

    const blue = ui.Color.hex(0x1144AA);
    t.color.accent = blue;                       // links, checked states, active tabs…
    t.color.accent_hover = ui.Color.hex(0x0D3688);
    t.color.accent_subtle = ui.Color.hex(0xE6ECF7);
    t.color.button_primary_bg = blue;            // primary buttons read these two,
    t.color.button_primary_fg = ui.Color.WHITE;  //   not accent
    t.color.border_focus = blue;
    t.color.selection_bg = ui.Color.hex(0xC9D6F0);
    t.color.list_selection_bg = ui.Color.hex(0xE6ECF7);

    t.radius.lg = 10;
    t.control.md.radius = 10;
    t.control.md.padding_h = 14;
    break :blk t;
};

pub const brand_dark: ui.ThemeTokens = blk: {
    var t = ui.theme.dark; // start from the dark preset, not from brand
    t.name = "brand_dark";
    t.scheme = .dark;      // Notification palettes and DevTools key off this

    const blue = ui.Color.hex(0x7FA2F0); // lighter on dark backgrounds
    t.color.accent = blue;
    t.color.button_primary_bg = blue;
    t.color.button_primary_fg = ui.Color.hex(0x0D1119);
    t.color.border_focus = blue;
    break :blk t;
};

const Prefs = struct {
    cx: *ui.Cx,
    dark: bool = false,

    pub fn toggle(self: *Prefs) void {
        self.dark = !self.dark;
        self.cx.setTheme(if (self.dark) &themes.brand_dark else &themes.brand);
    }
};

// In mountUI:
const prefs = try cx.bindState(Prefs, .{ .cx = cx });
cx.setTheme(&themes.brand);
// …
.on_click = cx.on(Prefs, prefs, Prefs.toggle),

// A reactive read of the current theme (lives as long as `scope`).
const theme_sig = try cx.themeSignal(scope);
const is_dark = theme_sig.get().scheme == .dark;