diff --git a/apps/web/src/components/ThemeProvider.tsx b/apps/web/src/components/ThemeProvider.tsx
index 331d5153..39cf8d1b 100644
--- a/apps/web/src/components/ThemeProvider.tsx
+++ b/apps/web/src/components/ThemeProvider.tsx
@@ -1,4 +1,18 @@
 import { createContext, useCallback, useContext, useEffect, useMemo, useState, type ReactNode } from "react";
+import {
+  DEFAULT_CUSTOM_DARK_COLORS,
+  DEFAULT_CUSTOM_EDITOR_THEME,
+  DEFAULT_CUSTOM_LIGHT_COLORS,
+  type CustomEditorTheme,
+  type ThemeColors,
+} from "@/lib/custom-editor-theme";
+
+export {
+  DEFAULT_CUSTOM_DARK_COLORS,
+  DEFAULT_CUSTOM_EDITOR_THEME,
+  DEFAULT_CUSTOM_LIGHT_COLORS,
+} from "@/lib/custom-editor-theme";
+export type { CustomEditorTheme, ThemeColors } from "@/lib/custom-editor-theme";
 
 export type ThemePreference = "system" | "light" | "dark";
 export type ResolvedTheme = "light" | "dark";
@@ -84,52 +98,6 @@ export const EDITOR_THEME_NAMES = [
 ] as const;
 export type EditorThemeName = string;
 
-export interface ThemeColors {
-  background: string;
-  text: string;
-  muted: string;
-  heading: string;
-  accent: string;
-  soft: string;
-  border: string;
-}
-
-export interface CustomEditorTheme {
-  id: string;
-  name: string;
-  light: ThemeColors;
-  dark: ThemeColors;
-  customCss?: string;
-}
-
-export const DEFAULT_CUSTOM_LIGHT_COLORS: ThemeColors = {
-  background: "#fffdf7",
-  text: "#292524",
-  muted: "#57534e",
-  heading: "#1c1917",
-  accent: "#0f766e",
-  soft: "#f0fdfa",
-  border: "#99f6e4",
-};
-
-export const DEFAULT_CUSTOM_DARK_COLORS: ThemeColors = {
-  background: "#1c1917",
-  text: "#fafaf9",
-  muted: "#d6d3d1",
-  heading: "#fafaf9",
-  accent: "#2dd4bf",
-  soft: "#292524",
-  border: "#44403c",
-};
-
-export const DEFAULT_CUSTOM_EDITOR_THEME: CustomEditorTheme = {
-  id: "custom-default",
-  name: "My custom theme",
-  light: DEFAULT_CUSTOM_LIGHT_COLORS,
-  dark: DEFAULT_CUSTOM_DARK_COLORS,
-  customCss: "",
-};
-
 interface AppearanceThemeContextValue {
   preference: ThemePreference;
   resolvedTheme: ResolvedTheme;
diff --git a/apps/web/src/components/settings/CustomEditorThemeDialog.tsx b/apps/web/src/components/settings/CustomEditorThemeDialog.tsx
index 41a1c347..e381fa53 100644
--- a/apps/web/src/components/settings/CustomEditorThemeDialog.tsx
+++ b/apps/web/src/components/settings/CustomEditorThemeDialog.tsx
@@ -1,5 +1,5 @@
-import { useEffect, useState } from "react";
-import { RotateCcw, Sun, Moon } from "lucide-react";
+import { useEffect, useRef, useState } from "react";
+import { Download, Moon, RotateCcw, Sun, Upload } from "lucide-react";
 import { useTranslation } from "react-i18next";
 import { Button } from "@/components/ui/button";
 import {
@@ -12,13 +12,19 @@ import {
 } from "@/components/ui/dialog";
 import { Input } from "@/components/ui/input";
 import { sanitizeAndScopeCss } from "@/lib/css-sandbox";
-import { contrastRatio } from "@/lib/color-contrast";
 import {
+  CustomEditorThemeFileError,
   DEFAULT_CUSTOM_LIGHT_COLORS,
   DEFAULT_CUSTOM_DARK_COLORS,
+  MAX_CUSTOM_EDITOR_THEME_FILE_BYTES,
+  customEditorThemeFileName,
+  getEditorThemeContrastIssues,
+  isValidThemeColors,
+  parseCustomEditorThemeFile,
+  serializeCustomEditorTheme,
   type CustomEditorTheme,
   type ThemeColors,
-} from "../ThemeProvider";
+} from "@/lib/custom-editor-theme";
 
 interface CustomEditorThemeDialogProps {
   open: boolean;
@@ -39,12 +45,6 @@ const COLOR_FIELDS = [
   ["border", "settings.customEditorTheme.border"],
 ] as const;
 
-const hasAccessibleContrast = (colors: ThemeColors) =>
-  contrastRatio(colors.text, colors.background) >= 4.5 &&
-  contrastRatio(colors.muted, colors.soft) >= 4.5 &&
-  contrastRatio(colors.heading, colors.background) >= 4.5 &&
-  contrastRatio(colors.accent, colors.background) >= 3;
-
 export const CustomEditorThemeDialog = ({
   open,
   theme,
@@ -53,14 +53,17 @@ export const CustomEditorThemeDialog = ({
   onDelete,
   isDefaultTheme = false,
 }: CustomEditorThemeDialogProps) => {
-  const { t } = useTranslation();
+  const { t, i18n } = useTranslation();
+  const fileInputRef = useRef<HTMLInputElement>(null);
   const [draft, setDraft] = useState<CustomEditorTheme>(theme);
   const [activeMode, setActiveMode] = useState<"light" | "dark">("light");
+  const [importError, setImportError] = useState<string | null>(null);
 
   useEffect(() => {
     if (open) {
       setDraft(theme);
       setActiveMode("light");
+      setImportError(null);
     }
   }, [open, theme]);
 
@@ -79,15 +82,48 @@ export const CustomEditorThemeDialog = ({
   const activeColors = draft[activeMode] || DEFAULT_CUSTOM_LIGHT_COLORS;
   const defaultColors = activeMode === "light" ? DEFAULT_CUSTOM_LIGHT_COLORS : DEFAULT_CUSTOM_DARK_COLORS;
 
-  const validColors = (colors: ThemeColors) =>
-    COLOR_FIELDS.every(([key]) => /^#[0-9a-f]{6}$/i.test(colors[key]));
-
   const valid =
     draft.name.trim().length > 0 &&
-    validColors(draft.light) &&
-    validColors(draft.dark) &&
-    hasAccessibleContrast(draft.light) &&
-    hasAccessibleContrast(draft.dark);
+    isValidThemeColors(draft.light) &&
+    isValidThemeColors(draft.dark);
+  const lightContrastIssues = isValidThemeColors(draft.light) ? getEditorThemeContrastIssues(draft.light) : [];
+  const darkContrastIssues = isValidThemeColors(draft.dark) ? getEditorThemeContrastIssues(draft.dark) : [];
+  const activeContrastIssues = activeMode === "light" ? lightContrastIssues : darkContrastIssues;
+
+  const describeImportError = (error: unknown) => {
+    if (error instanceof CustomEditorThemeFileError) {
+      return t(`settings.customEditorTheme.importErrors.${error.code}`);
+    }
+    return t("settings.customEditorTheme.importErrors.invalidFile");
+  };
+
+  const handleImport = async (file: File | undefined) => {
+    if (!file) return;
+    setImportError(null);
+    try {
+      if (file.size > MAX_CUSTOM_EDITOR_THEME_FILE_BYTES) {
+        throw new CustomEditorThemeFileError("fileTooLarge", "Editor theme file is too large.");
+      }
+      const imported = parseCustomEditorThemeFile(await file.text());
+      setDraft({ id: `custom-${crypto.randomUUID()}`, ...imported });
+      setActiveMode("light");
+    } catch (error) {
+      setImportError(describeImportError(error));
+    } finally {
+      if (fileInputRef.current) fileInputRef.current.value = "";
+    }
+  };
+
+  const handleExport = () => {
+    const url = URL.createObjectURL(new Blob([serializeCustomEditorTheme(draft)], { type: "application/json;charset=utf-8" }));
+    const anchor = document.createElement("a");
+    anchor.href = url;
+    anchor.download = customEditorThemeFileName(draft.name);
+    document.body.appendChild(anchor);
+    anchor.click();
+    anchor.remove();
+    window.setTimeout(() => URL.revokeObjectURL(url), 0);
+  };
 
   const handleReset = () => {
     setDraft((current) => ({
@@ -168,11 +204,16 @@ export const CustomEditorThemeDialog = ({
               </div>
             ))}
           </div>
-          {!valid && validColors(draft.light) && validColors(draft.dark) ? (
+          {activeContrastIssues.length > 0 ? (
             <p className="rounded-md bg-amber-50 px-2.5 py-2 text-[11px] leading-4 text-amber-800">
-              {t("settings.customEditorTheme.contrastWarning")}
+              {t("settings.customEditorTheme.contrastWarning", {
+                mode: t(`settings.customEditorTheme.modes.${activeMode}`),
+                fields: new Intl.ListFormat(i18n.resolvedLanguage ?? i18n.language, { type: "conjunction" })
+                  .format(activeContrastIssues.map((field) => t(`settings.customEditorTheme.${field}`))),
+              })}
             </p>
           ) : null}
+          {importError ? <p className="rounded-md bg-red-50 px-2.5 py-2 text-[11px] leading-4 text-red-700" role="alert">{importError}</p> : null}
 
           {/* Custom CSS Textarea */}
           <label className="grid gap-1 text-xs font-semibold text-slate-700">
@@ -218,10 +259,25 @@ export const CustomEditorThemeDialog = ({
         </div>
         <DialogFooter className="gap-2 sm:gap-0 mt-3 pt-2 border-t border-slate-100">
           <div className="flex flex-1 gap-2">
-            <Button variant="ghost" size="sm" className="h-8 px-2.5 text-xs text-slate-500 hover:text-slate-800" onClick={handleReset} title={t("settings.customEditorTheme.reset")}>
+            <Button variant="ghost" size="sm" className="h-8 px-2.5 text-xs text-slate-500 hover:text-slate-800" onClick={handleReset}>
               <RotateCcw className="h-3.5 w-3.5 mr-1" />
               {t("settings.customEditorTheme.reset")}
             </Button>
+            <Button variant="ghost" size="sm" className="h-8 px-2.5 text-xs text-slate-500 hover:text-slate-800" onClick={() => fileInputRef.current?.click()}>
+              <Upload className="h-3.5 w-3.5 mr-1" />
+              {t("settings.customEditorTheme.import")}
+            </Button>
+            <Button variant="ghost" size="sm" className="h-8 px-2.5 text-xs text-slate-500 hover:text-slate-800" disabled={!valid} onClick={handleExport}>
+              <Download className="h-3.5 w-3.5 mr-1" />
+              {t("settings.customEditorTheme.export")}
+            </Button>
+            <input
+              ref={fileInputRef}
+              className="hidden"
+              type="file"
+              accept=".json,application/json"
+              onChange={(event) => void handleImport(event.target.files?.[0])}
+            />
             {onDelete && !isDefaultTheme && (
               <Button
                 variant="danger"
diff --git a/apps/web/src/components/settings/PreferenceCard.test.mjs b/apps/web/src/components/settings/PreferenceCard.test.mjs
index 1515f6ac..36e956e0 100644
--- a/apps/web/src/components/settings/PreferenceCard.test.mjs
+++ b/apps/web/src/components/settings/PreferenceCard.test.mjs
@@ -11,3 +11,14 @@ describe("editor content alignment preference", () => {
     expect(editorPane).not.toContain("onToggleEditorContentAlignment");
   });
 });
+
+describe("custom editor theme portability", () => {
+  test("offers import and export while keeping contrast as a warning", () => {
+    const dialog = readFileSync(new URL("./CustomEditorThemeDialog.tsx", import.meta.url), "utf8");
+
+    expect(dialog).toContain('t("settings.customEditorTheme.import")');
+    expect(dialog).toContain('t("settings.customEditorTheme.export")');
+    expect(dialog).toContain("activeContrastIssues.length > 0");
+    expect(dialog).not.toContain("hasAccessibleContrast(draft.light)");
+  });
+});
diff --git a/apps/web/src/lib/custom-editor-theme.test.mjs b/apps/web/src/lib/custom-editor-theme.test.mjs
new file mode 100644
index 00000000..ddb5efa0
--- /dev/null
+++ b/apps/web/src/lib/custom-editor-theme.test.mjs
@@ -0,0 +1,76 @@
+import { describe, expect, test } from "bun:test";
+import {
+  CUSTOM_EDITOR_THEME_FILE_SCHEMA,
+  CUSTOM_EDITOR_THEME_FILE_VERSION,
+  CustomEditorThemeFileError,
+  customEditorThemeFileName,
+  getEditorThemeContrastIssues,
+  parseCustomEditorThemeFile,
+  serializeCustomEditorTheme,
+} from "./custom-editor-theme.ts";
+
+const theme = {
+  id: "custom-local-only",
+  name: "Calm / Green",
+  light: {
+    background: "#ffffff",
+    text: "#111111",
+    muted: "#444444",
+    heading: "#000000",
+    accent: "#087f5b",
+    soft: "#f1f5f9",
+    border: "#cbd5e1",
+  },
+  dark: {
+    background: "#111111",
+    text: "#f8fafc",
+    muted: "#cbd5e1",
+    heading: "#ffffff",
+    accent: "#34d399",
+    soft: "#1f2937",
+    border: "#475569",
+  },
+  customCss: "h1 { font-style: italic; }",
+};
+
+describe("custom editor theme files", () => {
+  test("round-trips a versioned theme without exporting its local id", () => {
+    const serialized = serializeCustomEditorTheme(theme);
+    const document = JSON.parse(serialized);
+
+    expect(document.schema).toBe(CUSTOM_EDITOR_THEME_FILE_SCHEMA);
+    expect(document.version).toBe(CUSTOM_EDITOR_THEME_FILE_VERSION);
+    expect(document.id).toBeUndefined();
+    expect(parseCustomEditorThemeFile(serialized)).toEqual({
+      name: theme.name,
+      light: theme.light,
+      dark: theme.dark,
+      customCss: theme.customCss,
+    });
+  });
+
+  test("rejects invalid colors and unsupported versions", () => {
+    const invalidColor = JSON.parse(serializeCustomEditorTheme(theme));
+    invalidColor.light.text = "red";
+    expect(() => parseCustomEditorThemeFile(JSON.stringify(invalidColor))).toThrow(CustomEditorThemeFileError);
+
+    const unsupported = JSON.parse(serializeCustomEditorTheme(theme));
+    unsupported.version = 2;
+    try {
+      parseCustomEditorThemeFile(JSON.stringify(unsupported));
+      throw new Error("Expected an unsupported version error");
+    } catch (error) {
+      expect(error).toBeInstanceOf(CustomEditorThemeFileError);
+      expect(error.code).toBe("unsupportedVersion");
+    }
+  });
+
+  test("reports low contrast without making the theme structurally invalid", () => {
+    expect(getEditorThemeContrastIssues({ ...theme.light, text: "#fefefe", accent: "#eeeeee" }))
+      .toEqual(["text", "accent"]);
+  });
+
+  test("creates a filesystem-safe descriptive filename", () => {
+    expect(customEditorThemeFileName(theme.name)).toBe("EdgeEver-Calm - Green.json");
+  });
+});
diff --git a/apps/web/src/lib/custom-editor-theme.ts b/apps/web/src/lib/custom-editor-theme.ts
new file mode 100644
index 00000000..0db89a5e
--- /dev/null
+++ b/apps/web/src/lib/custom-editor-theme.ts
@@ -0,0 +1,139 @@
+import { contrastRatio } from "./color-contrast";
+
+export interface ThemeColors {
+  background: string;
+  text: string;
+  muted: string;
+  heading: string;
+  accent: string;
+  soft: string;
+  border: string;
+}
+
+export interface CustomEditorTheme {
+  id: string;
+  name: string;
+  light: ThemeColors;
+  dark: ThemeColors;
+  customCss?: string;
+}
+
+export const DEFAULT_CUSTOM_LIGHT_COLORS: ThemeColors = {
+  background: "#fffdf7",
+  text: "#292524",
+  muted: "#57534e",
+  heading: "#1c1917",
+  accent: "#0f766e",
+  soft: "#f0fdfa",
+  border: "#99f6e4",
+};
+
+export const DEFAULT_CUSTOM_DARK_COLORS: ThemeColors = {
+  background: "#1c1917",
+  text: "#fafaf9",
+  muted: "#d6d3d1",
+  heading: "#fafaf9",
+  accent: "#2dd4bf",
+  soft: "#292524",
+  border: "#44403c",
+};
+
+export const DEFAULT_CUSTOM_EDITOR_THEME: CustomEditorTheme = {
+  id: "custom-default",
+  name: "My custom theme",
+  light: DEFAULT_CUSTOM_LIGHT_COLORS,
+  dark: DEFAULT_CUSTOM_DARK_COLORS,
+  customCss: "",
+};
+
+export const CUSTOM_EDITOR_THEME_FILE_SCHEMA = "edgeever.editor-theme";
+export const CUSTOM_EDITOR_THEME_FILE_VERSION = 1;
+export const MAX_CUSTOM_EDITOR_THEME_FILE_BYTES = 64 * 1024;
+export const MAX_CUSTOM_EDITOR_THEME_CSS_LENGTH = 2000;
+
+const COLOR_FIELDS = ["background", "text", "muted", "heading", "accent", "soft", "border"] as const;
+const HEX_COLOR_PATTERN = /^#[0-9a-f]{6}$/i;
+
+type PortableCustomEditorTheme = Omit<CustomEditorTheme, "id">;
+
+export type EditorThemeContrastIssue = "text" | "muted" | "heading" | "accent";
+export type CustomEditorThemeFileErrorCode = "invalidFile" | "unsupportedVersion" | "fileTooLarge";
+
+export class CustomEditorThemeFileError extends Error {
+  readonly code: CustomEditorThemeFileErrorCode;
+
+  constructor(code: CustomEditorThemeFileErrorCode, message: string) {
+    super(message);
+    this.name = "CustomEditorThemeFileError";
+    this.code = code;
+  }
+}
+
+const isRecord = (value: unknown): value is Record<string, unknown> =>
+  typeof value === "object" && value !== null && !Array.isArray(value);
+
+export const isValidThemeColors = (value: unknown): value is ThemeColors =>
+  isRecord(value) && COLOR_FIELDS.every((field) => typeof value[field] === "string" && HEX_COLOR_PATTERN.test(value[field]));
+
+export const getEditorThemeContrastIssues = (colors: ThemeColors): EditorThemeContrastIssue[] => {
+  const issues: EditorThemeContrastIssue[] = [];
+  if (contrastRatio(colors.text, colors.background) < 4.5) issues.push("text");
+  if (contrastRatio(colors.muted, colors.soft) < 4.5) issues.push("muted");
+  if (contrastRatio(colors.heading, colors.background) < 4.5) issues.push("heading");
+  if (contrastRatio(colors.accent, colors.background) < 3) issues.push("accent");
+  return issues;
+};
+
+export const serializeCustomEditorTheme = (theme: CustomEditorTheme) => JSON.stringify({
+  schema: CUSTOM_EDITOR_THEME_FILE_SCHEMA,
+  version: CUSTOM_EDITOR_THEME_FILE_VERSION,
+  name: theme.name,
+  light: theme.light,
+  dark: theme.dark,
+  customCss: theme.customCss ?? "",
+}, null, 2);
+
+export const parseCustomEditorThemeFile = (source: string): PortableCustomEditorTheme => {
+  if (new TextEncoder().encode(source).byteLength > MAX_CUSTOM_EDITOR_THEME_FILE_BYTES) {
+    throw new CustomEditorThemeFileError("fileTooLarge", "Editor theme file is too large.");
+  }
+
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(source);
+  } catch {
+    throw new CustomEditorThemeFileError("invalidFile", "Editor theme file must contain valid JSON.");
+  }
+  if (!isRecord(parsed) || parsed.schema !== CUSTOM_EDITOR_THEME_FILE_SCHEMA) {
+    throw new CustomEditorThemeFileError("invalidFile", "Editor theme file has an invalid schema.");
+  }
+  if (parsed.version !== CUSTOM_EDITOR_THEME_FILE_VERSION) {
+    throw new CustomEditorThemeFileError("unsupportedVersion", "Editor theme file version is not supported.");
+  }
+  if (typeof parsed.name !== "string" || parsed.name.trim().length === 0 || parsed.name.trim().length > 32) {
+    throw new CustomEditorThemeFileError("invalidFile", "Editor theme name must contain 1 to 32 characters.");
+  }
+  if (!isValidThemeColors(parsed.light) || !isValidThemeColors(parsed.dark)) {
+    throw new CustomEditorThemeFileError("invalidFile", "Editor theme colors must use six-digit hex values.");
+  }
+  if (parsed.customCss !== undefined && (typeof parsed.customCss !== "string" || parsed.customCss.length > MAX_CUSTOM_EDITOR_THEME_CSS_LENGTH)) {
+    throw new CustomEditorThemeFileError("invalidFile", "Editor theme CSS is invalid or too long.");
+  }
+
+  return {
+    name: parsed.name.trim(),
+    light: parsed.light,
+    dark: parsed.dark,
+    customCss: parsed.customCss ?? "",
+  };
+};
+
+export const customEditorThemeFileName = (name: string) => {
+  const safeName = name
+    .trim()
+    .replace(/[\u0000-\u001f<>:"/\\|?*]+/g, "-")
+    .replace(/\s+/g, " ")
+    .replace(/[. ]+$/g, "")
+    .slice(0, 80) || "custom-theme";
+  return `EdgeEver-${safeName}.json`;
+};
diff --git a/packages/shared/src/i18n/en-US.ts b/packages/shared/src/i18n/en-US.ts
index 55ff945d..1cd7abbb 100644
--- a/packages/shared/src/i18n/en-US.ts
+++ b/packages/shared/src/i18n/en-US.ts
@@ -269,6 +269,8 @@ export const enUS = {
       title: "Custom editor theme",
       description: "Adjust editor colors. This setting is saved in the current browser.",
       edit: "Edit colors",
+      import: "Import",
+      export: "Export",
       reset: "Restore defaults",
       name: "Theme name",
       background: "Background",
@@ -282,7 +284,16 @@ export const enUS = {
       previewBody: "This is a body text preview to help you evaluate the color combination.",
       previewMuted: "Muted supporting text should remain clear on the soft background.",
       previewAccent: "Accent text",
-      contrastWarning: "Body, muted, heading, or accent colors need more contrast before saving.",
+      contrastWarning: "{{fields}} have low contrast in {{mode}}. You can still save this theme.",
+      modes: {
+        light: "light mode",
+        dark: "dark mode",
+      },
+      importErrors: {
+        invalidFile: "Import failed: this is not a valid EdgeEver editor theme file.",
+        unsupportedVersion: "Import failed: this editor theme file version is not supported.",
+        fileTooLarge: "Import failed: the editor theme file exceeds 64 KiB.",
+      },
     },
     mermaidThemes: {
       auto: "Follow app appearance",
diff --git a/packages/shared/src/i18n/zh-CN.ts b/packages/shared/src/i18n/zh-CN.ts
index 529ede04..5800cb36 100644
--- a/packages/shared/src/i18n/zh-CN.ts
+++ b/packages/shared/src/i18n/zh-CN.ts
@@ -269,6 +269,8 @@ export const zhCN = {
       title: "自定义编辑器主题",
       description: "调整正文编辑区的颜色，设置仅保存在当前浏览器中。",
       edit: "编辑配色",
+      import: "导入",
+      export: "导出",
       reset: "恢复默认",
       name: "主题名称",
       background: "背景色",
@@ -282,7 +284,16 @@ export const zhCN = {
       previewBody: "这是一段正文预览，用来感受背景、文字和边框的组合效果。",
       previewMuted: "辅助说明文字需要在柔和背景上保持清晰。",
       previewAccent: "强调文字",
-      contrastWarning: "正文、辅助文字、标题或强调色的对比度不足，请调整后保存。",
+      contrastWarning: "{{mode}}的{{fields}}对比度较低；你仍可保存此主题。",
+      modes: {
+        light: "浅色模式",
+        dark: "深色模式",
+      },
+      importErrors: {
+        invalidFile: "无法导入：文件不是有效的 EdgeEver 编辑器主题。",
+        unsupportedVersion: "无法导入：该主题文件版本暂不受支持。",
+        fileTooLarge: "无法导入：主题文件超过 64 KiB。",
+      },
     },
     mermaidThemes: {
       auto: "跟随应用外观",