diff --git a/src/components/Dropdown.tsx b/src/components/Dropdown.tsx
new file mode 100644
index 0000000..da6009a
--- /dev/null
+++ b/src/components/Dropdown.tsx
@@ -0,0 +1,73 @@
+// 自绘下拉（替代原生 select：原生展开层是系统样式，与应用风格脱节）。
+// 外观对齐 .input；展开层沿用应用菜单语言（面板底、6px 圆角、悬停 --hover、
+// 选中 --accent-weak）；点别处/Esc 关闭走统一的 useDismiss；支持上下键选行。
+import { useEffect, useRef, useState } from 'react'
+import { useDismiss } from '../hooks/useDismiss'
+
+export interface DropdownOption { value: string; label: string }
+
+export function Dropdown({ value, options, onChange, disabled, ariaLabel }: {
+  value: string
+  options: DropdownOption[]
+  onChange: (value: string) => void
+  disabled?: boolean
+  ariaLabel?: string
+}) {
+  const [open, setOpen] = useState(false)
+  const ref = useRef<HTMLDivElement>(null)
+  const menuRef = useRef<HTMLDivElement>(null)
+  useDismiss(ref, open, () => setOpen(false))
+
+  const current = options.find((o) => o.value === value) ?? options[0]
+
+  // 打开时把焦点放到选中项，便于直接上下键选行
+  useEffect(() => {
+    if (!open) return
+    const idx = Math.max(0, options.findIndex((o) => o.value === value))
+    menuRef.current?.querySelectorAll('button')[idx]?.focus()
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [open ])
+
+  const pick = (v: string) => { setOpen(false); onChange(v) }
+
+  const onMenuKey = (e: React.KeyboardEvent) => {
+    if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp') return
+    e.preventDefault()
+    const buttons = [...(menuRef.current?.querySelectorAll('button') ?? [])]
+    const idx = buttons.indexOf(document.activeElement as HTMLButtonElement)
+    const next = e.key === 'ArrowDown'
+      ? Math.min(buttons.length - 1, idx + 1)
+      : Math.max(0, idx - 1)
+    buttons[next]?.focus()
+  }
+
+  return (
+    <div className="dropdown" ref={ref}>
+      <button
+        type="button"
+        className="dropdown-button"
+        disabled={disabled}
+        aria-label={ariaLabel}
+        aria-expanded={open}
+        onClick={() => setOpen((o) => !o)}
+      >
+        <span className="dropdown-label">{current?.label ?? ''}</span>
+        <svg width="10" height="10" viewBox="0 0 10 10" aria-hidden="true"><path d="M2 3.5 L5 6.5 L8 3.5" fill="none" stroke="currentColor" strokeWidth="1.3" strokeLinecap="round" strokeLinejoin="round" /></svg>
+      </button>
+      {open && (
+        <div className="dropdown-menu" ref={menuRef} onKeyDown={onMenuKey}>
+          {options.map((o) => (
+            <button
+              key={o.value}
+              type="button"
+              className={o.value === value ? 'selected' : undefined}
+              onClick={() => pick(o.value)}
+            >
+              {o.label}
+            </button>
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}
diff --git a/src/components/Stage5Modals.tsx b/src/components/Stage5Modals.tsx
index 7a52709..cf5e96a 100644
--- a/src/components/Stage5Modals.tsx
+++ b/src/components/Stage5Modals.tsx
@@ -1,5 +1,6 @@
 import { useEffect } from 'react'
 import { DOC_THEMES } from '../themes'
+import { Dropdown } from './Dropdown'
 
 /** 外观与设置（阶段 5）：文档主题、当前文档临时主题、自定义 CSS、自动保存间隔。 */
 export function AppearanceModal({ docTheme, override, customCss, autosave, autosaveSeconds, hasTab, onDocTheme, onOverride, onCustomCss, onAutosave, onClose }: {
@@ -38,18 +39,18 @@ export function AppearanceModal({ docTheme, override, customCss, autosave, autos
             </button>
           ))}
         </div>
-        <label className="modal-field">
+        <div className="modal-field">
           <span>当前文档临时主题{hasTab ? '' : '（未打开文档）'}</span>
-          <select
-            className="input"
+          <Dropdown
             disabled={!hasTab}
             value={override ?? ''}
-            onChange={(e) => onOverride(e.target.value === '' ? null : e.target.value)}
-          >
-            <option value="">跟随全局主题</option>
-            {DOC_THEMES.map((t) => <option key={t.id} value={t.id}>{t.name}</option>)}
-          </select>
-        </label>
+            options={[
+              { value: '', label: '跟随全局主题' },
+              ...DOC_THEMES.map((t) => ({ value: t.id, label: t.name })),
+            ]}
+            onChange={(v) => onOverride(v === '' ? null : v)}
+          />
+        </div>
         <label className="modal-field">
           <span>自定义 CSS（即时生效；建议以 .milkdown 开头限定作用范围）</span>
           <textarea
diff --git a/src/styles.css b/src/styles.css
index 0edd8bf..b5d4e06 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -304,7 +304,18 @@ kbd { background: var(--code-bg); border: 1px solid var(--border); border-radius
 .modal-actions.left button { text-align: left; }
 .ws-search { display: flex; flex-direction: column; gap: 8px; padding: 10px; min-height: 0; }
 .ws-search-box { display: flex; gap: 6px; }
-.ws-search-box .input { flex: 1; min-width: 0; }
+.ws-search-box /* 自绘下拉（Dropdown 组件）：按钮对齐 .input，展开层沿用应用菜单语言 */
+.dropdown { position: relative; }
+.dropdown-button { width: 100%; display: flex; align-items: center; justify-content: space-between; gap: 8px; border: 1px solid var(--border); background: var(--bg); color: var(--text); border-radius: 6px; padding: 5px 9px; font-size: 13px; font-family: inherit; cursor: pointer; text-align: left; }
+.dropdown-button:hover:not(:disabled) { border-color: var(--accent); }
+.dropdown-button:disabled { opacity: 0.5; cursor: default; }
+.dropdown-button svg { flex: none; color: var(--text-dim); }
+.dropdown-label { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.dropdown-menu { position: absolute; top: calc(100% + 4px); left: 0; right: 0; z-index: 60; background: var(--bg-editor); border: 1px solid var(--border); border-radius: 8px; padding: 4px; box-shadow: 0 10px 28px rgba(0,0,0,0.18); display: flex; flex-direction: column; max-height: 264px; overflow-y: auto; }
+.dropdown-menu button { border: 0; background: transparent; color: var(--text); padding: 6px 9px; border-radius: 5px; font-size: 13px; font-family: inherit; text-align: left; cursor: pointer; }
+.dropdown-menu button:hover, .dropdown-menu button:focus-visible { background: var(--hover); outline: none; }
+.dropdown-menu button.selected { background: var(--accent-weak); }
+.input { flex: 1; min-width: 0; }
 .ws-search-case { font-size: 12px; color: var(--text-dim); display: flex; gap: 5px; align-items: center; }
 .ws-search-summary { font-size: 12px; color: var(--text-dim); }
 .ws-search-results { overflow-y: auto; display: flex; flex-direction: column; gap: 10px; }
diff --git a/tests/dropdown.test.tsx b/tests/dropdown.test.tsx
new file mode 100644
index 0000000..81aa0f8
--- /dev/null
+++ b/tests/dropdown.test.tsx
@@ -0,0 +1,40 @@
+// 自绘下拉回归：展开/选中/点别处关闭（替代原生 select）。
+import { describe, it, expect, vi } from 'vitest'
+import { createRoot } from 'react-dom/client'
+import { act } from 'react-dom/test-utils'
+import { Dropdown } from '../src/components/Dropdown'
+
+const OPTIONS = [
+  { value: '', label: '跟随全局主题' },
+  { value: 'github', label: 'GitHub' },
+  { value: 'notion', label: 'Notion' },
+]
+
+describe('Dropdown', () => {
+  it('展开列出选项且标出选中项；点击选项回调并关闭；点别处关闭', async () => {
+    const container = document.createElement('div')
+    document.body.appendChild(container)
+    const root = createRoot(container)
+    const onChange = vi.fn()
+    await act(async () => {
+      root.render(<Dropdown value="github" options={OPTIONS} onChange={onChange} />)
+    })
+    const button = container.querySelector('.dropdown-button') as HTMLButtonElement
+    expect(button.textContent).toContain('GitHub')
+    await act(async () => { button.dispatchEvent(new MouseEvent('click', { bubbles: true })) })
+    const menu = container.querySelector('.dropdown-menu')
+    expect(menu).not.toBeNull()
+    expect(menu?.querySelector('button.selected')?.textContent).toBe('GitHub')
+    const notion = [...menu!.querySelectorAll('button')].find((b) => b.textContent === 'Notion')
+    await act(async () => { notion?.dispatchEvent(new MouseEvent('click', { bubbles: true })) })
+    expect(onChange).toHaveBeenCalledWith('notion')
+    expect(container.querySelector('.dropdown-menu')).toBeNull()
+    // 再次展开，点别处关闭
+    await act(async () => { button.dispatchEvent(new MouseEvent('click', { bubbles: true })) })
+    expect(container.querySelector('.dropdown-menu')).not.toBeNull()
+    await act(async () => { document.body.dispatchEvent(new MouseEvent('mousedown', { bubbles: true })) })
+    expect(container.querySelector('.dropdown-menu')).toBeNull()
+    await act(async () => { root.unmount() })
+    container.remove()
+  })
+})