feat: add custom UI font support

Allow users to specify a custom font for the entire app interface
(menus, labels, buttons) separately from the terminal font. Supports
Google Fonts URLs, direct font file URLs, and local file paths.

- Add custom_ui_font_path and custom_ui_font_family to Rust config
- Refactor applyCustomFont into shared applyFontFromSource helper
- Add applyCustomUiFont function using --ui-font-family CSS variable
- Update app.css to use --ui-font-family with fallback
- Apply custom UI font on startup in +page.svelte
- Add Custom UI Font section to ConfigSidebar settings panel
- Add tests for applyCustomUiFont and setCustomUiFont

src-tauri/src/config.rs

@@ -145,12 +145,19 @@ pub struct HikariConfig {
     #[serde(default)]
     pub show_thinking_blocks: bool,
 
-    // Custom font settings
+    // Custom terminal font settings
     #[serde(default)]
     pub custom_font_path: Option<String>,
 
     #[serde(default)]
     pub custom_font_family: Option<String>,
+
+    // Custom UI font settings
+    #[serde(default)]
+    pub custom_ui_font_path: Option<String>,
+
+    #[serde(default)]
+    pub custom_ui_font_family: Option<String>,
 }
 
 impl Default for HikariConfig {
@@ -192,6 +199,8 @@ impl Default for HikariConfig {
             show_thinking_blocks: false,
             custom_font_path: None,
             custom_font_family: None,
+            custom_ui_font_path: None,
+            custom_ui_font_family: None,
         }
     }
 }
@@ -309,6 +318,8 @@ mod tests {
         assert!(!config.show_thinking_blocks);
         assert!(config.custom_font_path.is_none());
         assert!(config.custom_font_family.is_none());
+        assert!(config.custom_ui_font_path.is_none());
+        assert!(config.custom_ui_font_family.is_none());
     }
 
     #[test]
@@ -350,6 +361,8 @@ mod tests {
             show_thinking_blocks: true,
             custom_font_path: Some("/home/naomi/.fonts/MyFont.ttf".to_string()),
             custom_font_family: Some("MyFont".to_string()),
+            custom_ui_font_path: None,
+            custom_ui_font_family: None,
         };
 
         let json = serde_json::to_string(&config).unwrap();

src/app.css

@@ -154,11 +154,7 @@ body {
   padding: 0;
   height: 100%;
   overflow: hidden;
-  font-family:
-    "Segoe UI",
-    system-ui,
-    -apple-system,
-    sans-serif;
+  font-family: var(--ui-font-family, "Segoe UI", system-ui, -apple-system, sans-serif);
   background: var(--bg-primary);
   color: var(--text-primary);
 }

src/lib/components/ConfigSidebar.svelte

@@ -6,6 +6,7 @@
     type CustomThemeColors,
     applyFontSize,
     applyCustomFont,
+    applyCustomUiFont,
     applyCustomThemeColors,
     MIN_FONT_SIZE,
     MAX_FONT_SIZE,
@@ -63,12 +64,17 @@
     background_image_opacity: 0.3,
     custom_font_path: null,
     custom_font_family: null,
+    custom_ui_font_path: null,
+    custom_ui_font_family: null,
   });
 
   let showCustomThemeEditor = $state(false);
   let customFontPathInput = $state("");
   let customFontFamilyInput = $state("");
   let customFontStatus: string | null = $state(null);
+  let customUiFontPathInput = $state("");
+  let customUiFontFamilyInput = $state("");
+  let customUiFontStatus: string | null = $state(null);
 
   interface AuthStatus {
     is_logged_in: boolean;
@@ -96,6 +102,8 @@
     config = { ...c };
     customFontPathInput = c.custom_font_path ?? "";
     customFontFamilyInput = c.custom_font_family ?? "";
+    customUiFontPathInput = c.custom_ui_font_path ?? "";
+    customUiFontFamilyInput = c.custom_ui_font_family ?? "";
   });
 
   configStore.isSidebarOpen.subscribe((open) => {
@@ -1007,6 +1015,68 @@
         </p>
       </div>
 
+      <!-- Custom UI Font -->
+      <div class="mb-4">
+        <span class="block text-sm text-[var(--text-secondary)] mb-2">Custom UI Font</span>
+        <div class="flex flex-col gap-2">
+          <input
+            type="text"
+            bind:value={customUiFontPathInput}
+            placeholder="URL or local file path (e.g. /path/to/font.ttf)"
+            class="w-full px-3 py-2 text-sm rounded-lg border border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--text-primary)] placeholder-gray-500 focus:outline-none focus:border-[var(--accent-primary)]"
+          />
+          <input
+            type="text"
+            bind:value={customUiFontFamilyInput}
+            placeholder="Font family name (e.g. Inter)"
+            class="w-full px-3 py-2 text-sm rounded-lg border border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--text-primary)] placeholder-gray-500 focus:outline-none focus:border-[var(--accent-primary)]"
+          />
+          <div class="flex gap-2">
+            <button
+              onclick={async () => {
+                customUiFontStatus = null;
+                try {
+                  await configStore.setCustomUiFont(
+                    customUiFontPathInput || null,
+                    customUiFontFamilyInput || null
+                  );
+                  customUiFontStatus = "Font applied!";
+                } catch (e) {
+                  customUiFontStatus = `Error: ${e instanceof Error ? e.message : String(e)}`;
+                }
+              }}
+              class="flex-1 px-3 py-2 text-sm rounded-lg border border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--text-secondary)] hover:border-[var(--accent-primary)] transition-colors"
+            >
+              Apply UI Font
+            </button>
+            <button
+              onclick={async () => {
+                customUiFontStatus = null;
+                customUiFontPathInput = "";
+                customUiFontFamilyInput = "";
+                try {
+                  await configStore.setCustomUiFont(null, null);
+                  await applyCustomUiFont(null, null);
+                  customUiFontStatus = "Font reset to default.";
+                } catch (e) {
+                  customUiFontStatus = `Error: ${e instanceof Error ? e.message : String(e)}`;
+                }
+              }}
+              class="px-3 py-2 text-sm rounded-lg border border-[var(--border-color)] bg-[var(--bg-primary)] text-[var(--text-secondary)] hover:border-red-400 hover:text-red-400 transition-colors"
+            >
+              Reset
+            </button>
+          </div>
+          {#if customUiFontStatus}
+            <p class="text-xs text-[var(--text-tertiary)]">{customUiFontStatus}</p>
+          {/if}
+        </div>
+        <p class="text-xs text-[var(--text-tertiary)] mt-1">
+          Applies to the entire app interface (menus, labels, buttons). Supports Google Fonts URLs,
+          direct font file URLs, or local file paths.
+        </p>
+      </div>
+
       <!-- Show Thinking Blocks Toggle -->
       <div class="mb-4">
         <label class="flex items-center gap-3 cursor-pointer">

src/lib/components/StatusBar.svelte

@@ -113,6 +113,8 @@
     background_image_opacity: 0.3,
     custom_font_path: null,
     custom_font_family: null,
+    custom_ui_font_path: null,
+    custom_ui_font_family: null,
   });
 
   let streamerModeActive = $state(false);

src/lib/stores/config.test.ts

@@ -6,6 +6,7 @@ import {
   clampFontSize,
   applyFontSize,
   applyCustomFont,
+  applyCustomUiFont,
   applyTheme,
   applyCustomThemeColors,
   clearCustomThemeColors,
@@ -214,6 +215,8 @@ describe("config store", () => {
         background_image_opacity: 0.3,
         custom_font_path: null,
         custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       expect(config.model).toBe("claude-sonnet-4");
@@ -268,6 +271,8 @@ describe("config store", () => {
         background_image_opacity: 0.3,
         custom_font_path: null,
         custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       expect(config.model).toBeNull();
@@ -821,6 +826,8 @@ describe("config store", () => {
         background_image_opacity: 0.3,
         custom_font_path: null,
         custom_font_family: null,
+        custom_ui_font_path: null,
+        custom_ui_font_family: null,
       };
 
       const mockInvokeImpl = vi.mocked(invoke);
@@ -1317,4 +1324,133 @@ describe("config store", () => {
       );
     });
   });
+
+  describe("applyCustomUiFont", () => {
+    const readFileMock = vi.mocked(readFile);
+
+    beforeEach(() => {
+      document.getElementById("hikari-custom-ui-font")?.remove();
+      document.documentElement.style.removeProperty("--ui-font-family");
+      readFileMock.mockReset();
+    });
+
+    it("removes CSS variable when both path and family are null", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      await applyCustomUiFont(null, null);
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+    });
+
+    it("removes CSS variable when both path and family are empty strings", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      await applyCustomUiFont("", "");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+      expect(document.getElementById("hikari-custom-ui-font")).toBeNull();
+    });
+
+    it("injects @import for a CSS stylesheet URL", async () => {
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain(
+        "@import url('https://fonts.googleapis.com/css2?family=Inter')"
+      );
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+    });
+
+    it("injects @font-face for a direct font file URL (.woff2)", async () => {
+      await applyCustomUiFont("https://example.com/fonts/Inter.woff2", "Inter");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style).not.toBeNull();
+      expect(style?.textContent).toContain("@font-face");
+      expect(style?.textContent).toContain("url('https://example.com/fonts/Inter.woff2')");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+    });
+
+    it("uses HikariCustomUiFont as fallback family for direct font URLs when family is empty", async () => {
+      await applyCustomUiFont("https://example.com/fonts/Inter.woff2", "");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style?.textContent).toContain("'HikariCustomUiFont'");
+    });
+
+    it("reads local file and embeds as data URL", async () => {
+      const fakeData = new Uint8Array([104, 101, 108, 108, 111]);
+      readFileMock.mockResolvedValueOnce(fakeData);
+
+      await applyCustomUiFont("/home/naomi/.fonts/Inter.ttf", "Inter");
+
+      expect(readFileMock).toHaveBeenCalledWith("/home/naomi/.fonts/Inter.ttf");
+      const style = document.getElementById("hikari-custom-ui-font");
+      expect(style?.textContent).toContain("data:font/ttf;base64,");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+    });
+
+    it("sets CSS variable when only family is provided (no path)", async () => {
+      await applyCustomUiFont("", "SystemUiFont");
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'SystemUiFont', sans-serif"
+      );
+    });
+
+    it("replaces a previously injected style element", async () => {
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+      expect(document.getElementById("hikari-custom-ui-font")).not.toBeNull();
+
+      await applyCustomUiFont("https://fonts.googleapis.com/css2?family=Roboto", "Roboto");
+      const styles = document.querySelectorAll("#hikari-custom-ui-font");
+      expect(styles.length).toBe(1);
+      expect(styles[0].textContent).toContain("Roboto");
+    });
+  });
+
+  describe("setCustomUiFont", () => {
+    const readFileMock = vi.mocked(readFile);
+    const invokeMock = vi.mocked(invoke);
+
+    beforeEach(() => {
+      document.getElementById("hikari-custom-ui-font")?.remove();
+      document.documentElement.style.removeProperty("--ui-font-family");
+      readFileMock.mockReset();
+      invokeMock.mockResolvedValue(undefined);
+    });
+
+    it("saves config and applies the UI font", async () => {
+      await configStore.setCustomUiFont(null, null);
+      await configStore.setCustomUiFont("https://fonts.googleapis.com/css2?family=Inter", "Inter");
+
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_ui_font_path: "https://fonts.googleapis.com/css2?family=Inter",
+            custom_ui_font_family: "Inter",
+          }),
+        })
+      );
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe(
+        "'Inter', sans-serif"
+      );
+    });
+
+    it("clears UI font when called with nulls", async () => {
+      document.documentElement.style.setProperty("--ui-font-family", "'SomeFont', sans-serif");
+      await configStore.setCustomUiFont(null, null);
+
+      expect(document.documentElement.style.getPropertyValue("--ui-font-family")).toBe("");
+      expect(invokeMock).toHaveBeenCalledWith(
+        "save_config",
+        expect.objectContaining({
+          config: expect.objectContaining({
+            custom_ui_font_path: null,
+            custom_ui_font_family: null,
+          }),
+        })
+      );
+    });
+  });
 });

src/lib/stores/config.ts

@@ -59,9 +59,12 @@ export interface HikariConfig {
   // Background image settings
   background_image_path: string | null;
   background_image_opacity: number;
-  // Custom font settings
+  // Custom terminal font settings
   custom_font_path: string | null;
   custom_font_family: string | null;
+  // Custom UI font settings
+  custom_ui_font_path: string | null;
+  custom_ui_font_family: string | null;
 }
 
 const defaultConfig: HikariConfig = {
@@ -110,6 +113,8 @@ const defaultConfig: HikariConfig = {
   background_image_opacity: 0.3,
   custom_font_path: null,
   custom_font_family: null,
+  custom_ui_font_path: null,
+  custom_ui_font_family: null,
 };
 
 function createConfigStore() {
@@ -251,6 +256,11 @@ function createConfigStore() {
       await updateConfig({ custom_font_path: path, custom_font_family: family });
       await applyCustomFont(path, family);
     },
+
+    setCustomUiFont: async (path: string | null, family: string | null) => {
+      await updateConfig({ custom_ui_font_path: path, custom_ui_font_family: family });
+      await applyCustomUiFont(path, family);
+    },
   };
 }
 
@@ -316,66 +326,93 @@ export function clampFontSize(size: number): number {
   return Math.max(MIN_FONT_SIZE, Math.min(MAX_FONT_SIZE, size));
 }
 
-const FONT_STYLE_ID = "hikari-custom-font";
-const FONT_CSS_VAR = "--terminal-font-family";
 const DIRECT_FONT_EXTENSIONS = new Set(["woff", "woff2", "ttf", "otf", "eot"]);
 
+const FONT_MIME_MAP: Record<string, string> = {
+  woff: "font/woff",
+  woff2: "font/woff2",
+  ttf: "font/ttf",
+  otf: "font/otf",
+  eot: "application/vnd.ms-fontobject",
+};
+
+async function applyFontFromSource(path: string, family: string, styleId: string): Promise<void> {
+  const style = document.createElement("style");
+  style.id = styleId;
+
+  if (path.startsWith("http://") || path.startsWith("https://")) {
+    const ext = path.split(".").pop()?.toLowerCase() ?? "";
+
+    if (DIRECT_FONT_EXTENSIONS.has(ext)) {
+      style.textContent = `@font-face { font-family: '${family}'; src: url('${path}'); }`;
+    } else {
+      style.textContent = `@import url('${path}');`;
+    }
+  } else {
+    const data = await readFile(path);
+    const chunks: string[] = [];
+    const chunkSize = 8192;
+    for (let i = 0; i < data.length; i += chunkSize) {
+      chunks.push(String.fromCharCode(...data.slice(i, i + chunkSize)));
+    }
+    const ext = path.split(".").pop()?.toLowerCase() ?? "ttf";
+    const mime = FONT_MIME_MAP[ext] ?? "font/ttf";
+    const dataUrl = `data:${mime};base64,${btoa(chunks.join(""))}`;
+    style.textContent = `@font-face { font-family: '${family}'; src: url('${dataUrl}'); }`;
+  }
+
+  document.head.appendChild(style);
+}
+
 export async function applyCustomFont(path: string | null, family: string | null): Promise<void> {
   if (typeof document === "undefined") return;
 
-  // Remove any previously injected font style
-  document.getElementById(FONT_STYLE_ID)?.remove();
+  const styleId = "hikari-custom-font";
+  const cssVar = "--terminal-font-family";
+  const fallbackFamily = "HikariCustomFont";
+
+  document.getElementById(styleId)?.remove();
 
   const trimmedPath = path?.trim() ?? "";
   const trimmedFamily = family?.trim() ?? "";
 
   if (!trimmedPath && !trimmedFamily) {
-    document.documentElement.style.removeProperty(FONT_CSS_VAR);
+    document.documentElement.style.removeProperty(cssVar);
     return;
   }
 
   if (trimmedPath) {
-    const style = document.createElement("style");
-    style.id = FONT_STYLE_ID;
-
-    if (trimmedPath.startsWith("http://") || trimmedPath.startsWith("https://")) {
-      const ext = trimmedPath.split(".").pop()?.toLowerCase() ?? "";
-
-      if (DIRECT_FONT_EXTENSIONS.has(ext)) {
-        // Direct font file URL — inject via @font-face
-        const fontFamily = trimmedFamily || "HikariCustomFont";
-        style.textContent = `@font-face { font-family: '${fontFamily}'; src: url('${trimmedPath}'); }`;
-      } else {
-        // CSS stylesheet URL (e.g. Google Fonts) — inject as @import
-        style.textContent = `@import url('${trimmedPath}');`;
-      }
-    } else {
-      // Local file path — read via Tauri and embed as data URL
-      const data = await readFile(trimmedPath);
-      const chunks: string[] = [];
-      const chunkSize = 8192;
-      for (let i = 0; i < data.length; i += chunkSize) {
-        chunks.push(String.fromCharCode(...data.slice(i, i + chunkSize)));
-      }
-      const ext = trimmedPath.split(".").pop()?.toLowerCase() ?? "ttf";
-      const mimeMap: Record<string, string> = {
-        woff: "font/woff",
-        woff2: "font/woff2",
-        ttf: "font/ttf",
-        otf: "font/otf",
-        eot: "application/vnd.ms-fontobject",
-      };
-      const mime = mimeMap[ext] ?? "font/ttf";
-      const dataUrl = `data:${mime};base64,${btoa(chunks.join(""))}`;
-      const fontFamily = trimmedFamily || "HikariCustomFont";
-      style.textContent = `@font-face { font-family: '${fontFamily}'; src: url('${dataUrl}'); }`;
-    }
-
-    document.head.appendChild(style);
+    await applyFontFromSource(trimmedPath, trimmedFamily || fallbackFamily, styleId);
   }
 
   if (trimmedFamily) {
-    document.documentElement.style.setProperty(FONT_CSS_VAR, `'${trimmedFamily}', monospace`);
+    document.documentElement.style.setProperty(cssVar, `'${trimmedFamily}', monospace`);
+  }
+}
+
+export async function applyCustomUiFont(path: string | null, family: string | null): Promise<void> {
+  if (typeof document === "undefined") return;
+
+  const styleId = "hikari-custom-ui-font";
+  const cssVar = "--ui-font-family";
+  const fallbackFamily = "HikariCustomUiFont";
+
+  document.getElementById(styleId)?.remove();
+
+  const trimmedPath = path?.trim() ?? "";
+  const trimmedFamily = family?.trim() ?? "";
+
+  if (!trimmedPath && !trimmedFamily) {
+    document.documentElement.style.removeProperty(cssVar);
+    return;
+  }
+
+  if (trimmedPath) {
+    await applyFontFromSource(trimmedPath, trimmedFamily || fallbackFamily, styleId);
+  }
+
+  if (trimmedFamily) {
+    document.documentElement.style.setProperty(cssVar, `'${trimmedFamily}', sans-serif`);
   }
 }
 

src/routes/+page.svelte

@@ -16,6 +16,7 @@
     applyTheme,
     applyFontSize,
     applyCustomFont,
+    applyCustomUiFont,
     isCompactMode,
   } from "$lib/stores/config";
   import { readFile } from "@tauri-apps/plugin-fs";
@@ -461,6 +462,7 @@
       applyTheme(config.theme, config.custom_theme_colors);
       applyFontSize(config.font_size);
       await applyCustomFont(config.custom_font_path, config.custom_font_family);
+      await applyCustomUiFont(config.custom_ui_font_path, config.custom_ui_font_family);
 
       // Apply always-on-top setting
       if (config.always_on_top) {