diff --git a/src/theme/__tests__/builtin-themes.test.ts b/src/theme/__tests__/builtin-themes.test.ts
new file mode 100644
index 00000000..2d6ba35c
--- /dev/null
+++ b/src/theme/__tests__/builtin-themes.test.ts
@@ -0,0 +1,75 @@
+import { describe, it, expect } from 'vitest';
+import { BUILTIN_THEMES, getBuiltinTheme } from '../builtin-themes';
+import { resolvePalette } from '../colors';
+import { DARK_COLORS, LIGHT_COLORS } from '../tokens';
+
+// Solid fills: RN paints screens, sheets and cards with these and has no
+// backdrop blur, so a translucent value would show the content underneath.
+const SOLID_FILLS = [
+  'background', 'surface', 'surfaceHover', 'surfaceActive', 'card',
+  'secondary', 'muted', 'accent', 'primaryBg', 'primaryBgHover', 'popover',
+] as const;
+
+describe('built-in themes', () => {
+  it('ships every webmail built-in theme except Flat fields, in webmail order', () => {
+    expect(BUILTIN_THEMES.map((t) => t.id)).toEqual([
+      'builtin-qui',
+      'builtin-nord',
+      'builtin-catppuccin',
+      'builtin-solarized',
+      'builtin-roundcube-elastic',
+      'builtin-aurora-glass',
+    ]);
+  });
+
+  it('defines the same tokens for light and dark in every theme', () => {
+    for (const theme of BUILTIN_THEMES) {
+      expect(Object.keys(theme.light).sort(), theme.id).toEqual(Object.keys(theme.dark).sort());
+    }
+  });
+
+  it('keeps solid-fill tokens opaque', () => {
+    for (const theme of BUILTIN_THEMES) {
+      for (const scheme of ['light', 'dark'] as const) {
+        for (const key of SOLID_FILLS) {
+          expect(theme[scheme][key], `${theme.id} ${scheme} ${key}`).toMatch(/^#[0-9a-f]{6}$/i);
+        }
+      }
+    }
+  });
+
+  it('applies the Roundcube Elastic tokens in light and dark', () => {
+    const light = resolvePalette('light', 'builtin-roundcube-elastic');
+    expect(light.primary).toBe('#37beff');
+    expect(light.text).toBe('#27353a');
+    expect(light.background).toBe('#ffffff');
+    const dark = resolvePalette('dark', 'builtin-roundcube-elastic');
+    expect(dark.background).toBe('#21292c');
+    expect(dark.surface).toBe('#2c373a');
+    expect(dark.unread).toBe('#b88a00');
+    // Tokens the webmail theme doesn't define keep the base palette.
+    expect(dark.starred).toBe(DARK_COLORS.starred);
+    expect(dark.calendar).toBe(DARK_COLORS.calendar);
+  });
+
+  it('flattens the Aurora Glass dark glass tokens onto its background', () => {
+    const dark = resolvePalette('dark', 'builtin-aurora-glass');
+    expect(dark.primary).toBe('#8b7bff');
+    expect(dark.background).toBe('#06070f');
+    // rgba(255, 255, 255, 0.06) over #06070f
+    expect(dark.surface).toBe('#15161d');
+    // rgba(139, 123, 255, 0.16) over #06070f
+    expect(dark.accent).toBe('#1b1a35');
+    // Overlays may stay translucent, as in the other themes.
+    expect(dark.selection).toBe('rgba(139, 123, 255, 0.22)');
+    const light = resolvePalette('light', 'builtin-aurora-glass');
+    expect(light.background).toBe('#eef1fb');
+    expect(light.tags).toBe(LIGHT_COLORS.tags);
+  });
+
+  it('falls back to the base palette for an unknown or cleared theme id', () => {
+    expect(getBuiltinTheme('builtin-flat-fields')).toBeNull();
+    expect(resolvePalette('dark', 'builtin-flat-fields')).toBe(DARK_COLORS);
+    expect(resolvePalette('light', null)).toBe(LIGHT_COLORS);
+  });
+});
diff --git a/src/theme/builtin-themes.ts b/src/theme/builtin-themes.ts
index 28cb3fad..c6fdbbcb 100644
--- a/src/theme/builtin-themes.ts
+++ b/src/theme/builtin-themes.ts
@@ -2,6 +2,20 @@
 // scripts in the parity work (2026-08-29). Each theme overrides the subset of
 // ThemePalette that the CSS defines; everything else keeps the base palette.
 // Regenerate rather than hand-edit when the webmail themes change.
+//
+// Mapping (webmail --color-* -> ThemePalette): primary -> primary,
+// primaryDark, textLink, navActive; ring -> primaryLight, borderFocus;
+// accent -> primaryBg, primaryBgHover, surfaceHover; secondary -> surface;
+// muted -> surfaceActive; foreground -> text; background -> textInverse;
+// muted-foreground -> textSecondary, textMuted, read, navInactive;
+// destructive -> error, navBadge; border -> borderLight; the rest by name.
+// Translucent values of the solid-fill tokens (surfaces, cards, accent,
+// popover) are composited onto the theme background, because RN has no
+// backdrop blur and would show whatever lies underneath (Aurora Glass dark).
+//
+// Only the colour tokens are ported. The webmail's theme skins (fonts,
+// radii, Elastic's dark task rail, Aurora's gradient mesh and frosted panes)
+// and the "Flat fields" design-system theme have no native counterpart.
 import type { ThemePalette } from './tokens';
 
 export type PaletteOverride = Partial<Omit<ThemePalette, 'calendar' | 'tags'>>;
@@ -435,6 +449,216 @@ export const BUILTIN_THEMES: BuiltinTheme[] = [
       chart5: '#6c71c4',
     },
   },
+  {
+    id: 'builtin-roundcube-elastic',
+    name: 'Roundcube Elastic',
+    description: "Colours of Roundcube's Elastic skin: the #37beff blue on white or dark slate",
+    light: {
+      primary: '#37beff',
+      primaryDark: '#37beff',
+      primaryLight: '#37beff',
+      primaryBg: '#e6f6ff',
+      primaryBgHover: '#e6f6ff',
+      primaryForeground: '#ffffff',
+      background: '#ffffff',
+      surface: '#f4f4f4',
+      surfaceHover: '#e6f6ff',
+      surfaceActive: '#f4f4f4',
+      card: '#ffffff',
+      cardForeground: '#27353a',
+      text: '#27353a',
+      textSecondary: '#737677',
+      textMuted: '#737677',
+      textInverse: '#ffffff',
+      textLink: '#37beff',
+      border: '#dddddd',
+      borderLight: '#dddddd',
+      borderFocus: '#37beff',
+      success: '#41b849',
+      successForeground: '#ffffff',
+      warning: '#ffd452',
+      warningForeground: '#27353a',
+      error: '#ff5552',
+      errorForeground: '#ffffff',
+      info: '#37beff',
+      infoForeground: '#ffffff',
+      unread: '#ffd452',
+      read: '#737677',
+      navActive: '#37beff',
+      navInactive: '#737677',
+      navBadge: '#ff5552',
+      secondary: '#f4f4f4',
+      secondaryForeground: '#27353a',
+      muted: '#f4f4f4',
+      mutedForeground: '#737677',
+      accent: '#e6f6ff',
+      accentForeground: '#0070a8',
+      selection: '#ebf8ff',
+      selectionForeground: '#27353a',
+      popover: '#ffffff',
+      popoverForeground: '#27353a',
+      chart1: '#37beff',
+      chart2: '#41b849',
+      chart3: '#ffd452',
+      chart4: '#ff5552',
+      chart5: '#9b59b6',
+    },
+    dark: {
+      primary: '#37beff',
+      primaryDark: '#37beff',
+      primaryLight: '#37beff',
+      primaryBg: '#374549',
+      primaryBgHover: '#374549',
+      primaryForeground: '#ffffff',
+      background: '#21292c',
+      surface: '#2c373a',
+      surfaceHover: '#374549',
+      surfaceActive: '#2c373a',
+      card: '#1a2225',
+      cardForeground: '#ffffff',
+      text: '#ffffff',
+      textSecondary: '#b3bec1',
+      textMuted: '#b3bec1',
+      textInverse: '#21292c',
+      textLink: '#37beff',
+      border: '#4d6066',
+      borderLight: '#4d6066',
+      borderFocus: '#37beff',
+      success: '#41b849',
+      successForeground: '#ffffff',
+      warning: '#ffd452',
+      warningForeground: '#21292c',
+      error: '#ff5552',
+      errorForeground: '#ffffff',
+      info: '#37beff',
+      infoForeground: '#ffffff',
+      unread: '#b88a00',
+      read: '#b3bec1',
+      navActive: '#37beff',
+      navInactive: '#b3bec1',
+      navBadge: '#ff5552',
+      secondary: '#2c373a',
+      secondaryForeground: '#ffffff',
+      muted: '#2c373a',
+      mutedForeground: '#b3bec1',
+      accent: '#374549',
+      accentForeground: '#37beff',
+      selection: '#374549',
+      selectionForeground: '#37beff',
+      popover: '#161b1d',
+      popoverForeground: '#ffffff',
+      chart1: '#37beff',
+      chart2: '#41b849',
+      chart3: '#ffd452',
+      chart4: '#ff5552',
+      chart5: '#b48ead',
+    },
+  },
+  {
+    id: 'builtin-aurora-glass',
+    name: 'Aurora Glass',
+    description: 'Vibrant indigo and cyan accents on a cool lavender or near-black canvas',
+    light: {
+      primary: '#6d5cff',
+      primaryDark: '#6d5cff',
+      primaryLight: '#6d5cff',
+      primaryBg: '#e0e7ff',
+      primaryBgHover: '#e0e7ff',
+      primaryForeground: '#ffffff',
+      background: '#eef1fb',
+      surface: '#e3e7f7',
+      surfaceHover: '#e0e7ff',
+      surfaceActive: '#e7eaf6',
+      card: '#ffffff',
+      cardForeground: '#14162e',
+      text: '#14162e',
+      textSecondary: '#5b6080',
+      textMuted: '#5b6080',
+      textInverse: '#eef1fb',
+      textLink: '#6d5cff',
+      border: 'rgba(13, 18, 45, 0.10)',
+      borderLight: 'rgba(13, 18, 45, 0.10)',
+      borderFocus: '#6d5cff',
+      success: '#10b981',
+      successForeground: '#ffffff',
+      warning: '#f59e0b',
+      warningForeground: '#14162e',
+      error: '#f43f5e',
+      errorForeground: '#ffffff',
+      info: '#06b6d4',
+      infoForeground: '#ffffff',
+      unread: '#6d5cff',
+      read: '#5b6080',
+      navActive: '#6d5cff',
+      navInactive: '#5b6080',
+      navBadge: '#f43f5e',
+      secondary: '#e3e7f7',
+      secondaryForeground: '#14162e',
+      muted: '#e7eaf6',
+      mutedForeground: '#5b6080',
+      accent: '#e0e7ff',
+      accentForeground: '#4338ca',
+      selection: 'rgba(109, 92, 255, 0.14)',
+      selectionForeground: '#4338ca',
+      popover: '#ffffff',
+      popoverForeground: '#14162e',
+      chart1: '#6d5cff',
+      chart2: '#06b6d4',
+      chart3: '#ec4899',
+      chart4: '#f59e0b',
+      chart5: '#10b981',
+    },
+    dark: {
+      primary: '#8b7bff',
+      primaryDark: '#8b7bff',
+      primaryLight: '#8b7bff',
+      primaryBg: '#1b1a35',
+      primaryBgHover: '#1b1a35',
+      primaryForeground: '#ffffff',
+      background: '#06070f',
+      surface: '#15161d',
+      surfaceHover: '#1b1a35',
+      surfaceActive: '#12131b',
+      card: '#101119',
+      cardForeground: '#eef0ff',
+      text: '#eef0ff',
+      textSecondary: '#9aa0c4',
+      textMuted: '#9aa0c4',
+      textInverse: '#06070f',
+      textLink: '#8b7bff',
+      border: 'rgba(255, 255, 255, 0.08)',
+      borderLight: 'rgba(255, 255, 255, 0.08)',
+      borderFocus: '#8b7bff',
+      success: '#34d399',
+      successForeground: '#052e1f',
+      warning: '#fbbf24',
+      warningForeground: '#1a1405',
+      error: '#fb7185',
+      errorForeground: '#1a0b10',
+      info: '#22d3ee',
+      infoForeground: '#04222a',
+      unread: '#8b7bff',
+      read: '#9aa0c4',
+      navActive: '#8b7bff',
+      navInactive: '#9aa0c4',
+      navBadge: '#fb7185',
+      secondary: '#15161d',
+      secondaryForeground: '#eef0ff',
+      muted: '#12131b',
+      mutedForeground: '#9aa0c4',
+      accent: '#1b1a35',
+      accentForeground: '#c4bbff',
+      selection: 'rgba(139, 123, 255, 0.22)',
+      selectionForeground: '#c4bbff',
+      popover: '#12132a',
+      popoverForeground: '#eef0ff',
+      chart1: '#8b7bff',
+      chart2: '#22d3ee',
+      chart3: '#f472b6',
+      chart4: '#fbbf24',
+      chart5: '#34d399',
+    },
+  },
 ];
 
 export function getBuiltinTheme(id: string | null | undefined): BuiltinTheme | null {