diff --git a/Reader/Cache.cpp b/Reader/Cache.cpp
index c2f0fda..9f06781 100644
--- a/Reader/Cache.cpp
+++ b/Reader/Cache.cpp
@@ -366,6 +366,7 @@ void Cache::default_header(header_t* header)
     // default bk color
     header->bg_color = 0x00ffffff;  // White
     header->alpha = 0xff;
+    header->transparent_bg = 0;
 
     header->char_gap = 0;
     header->line_gap = 5;
diff --git a/Reader/DisplaySet.cpp b/Reader/DisplaySet.cpp
index 92ceafa..766fa02 100644
--- a/Reader/DisplaySet.cpp
+++ b/Reader/DisplaySet.cpp
@@ -23,6 +23,7 @@ typedef struct display_set_data_t
     int word_wrap;
     int line_indent;
     int blank_lines;
+    int transparent_bg;
     int chapter_page;
     int is_save;
 } display_set_data_t;
@@ -80,6 +81,7 @@ static void _update_preview(HDC hDC, RECT *rc);
     (d)->word_wrap = (s)->word_wrap; \
     (d)->line_indent = (s)->line_indent; \
     (d)->blank_lines = (s)->blank_lines; \
+    (d)->transparent_bg = (s)->transparent_bg; \
     (d)->chapter_page = (s)->chapter_page;
 
 void OpenDisplaySetDlg(void)
@@ -224,6 +226,10 @@ static INT_PTR CALLBACK DisplaySetDlgProc(HWND hDlg, UINT message, WPARAM wParam
             res = (int)SendMessage(GetDlgItem(hDlg, IDC_CHECK_BLANKLINES), BM_GETCHECK, 0, NULL);
             _display.blank_lines = BST_CHECKED == res ? 1 : 0;
             break;
+        case IDC_CHECK_TRANS_BG:
+            res = (int)SendMessage(GetDlgItem(hDlg, IDC_CHECK_TRANS_BG), BM_GETCHECK, 0, NULL);
+            _display.transparent_bg = BST_CHECKED == res ? 1 : 0;
+            break;
         case IDC_CHECK_CHAPTER_PAGE:
             res = (int)SendMessage(GetDlgItem(hDlg, IDC_CHECK_CHAPTER_PAGE), BM_GETCHECK, 0, NULL);
             _display.chapter_page = BST_CHECKED == res ? 1 : 0;
@@ -315,6 +321,7 @@ static void _init_layout_set(HWND hDlg)
     SendMessage(GetDlgItem(hDlg, IDC_CHECK_WORD_WRAP), BM_SETCHECK, _display.word_wrap ? BST_CHECKED : BST_UNCHECKED, NULL);
     SendMessage(GetDlgItem(hDlg, IDC_CHECK_INDENT), BM_SETCHECK, _display.line_indent ? BST_CHECKED : BST_UNCHECKED, NULL);
     SendMessage(GetDlgItem(hDlg, IDC_CHECK_BLANKLINES), BM_SETCHECK, _display.blank_lines ? BST_CHECKED : BST_UNCHECKED, NULL);
+    SendMessage(GetDlgItem(hDlg, IDC_CHECK_TRANS_BG), BM_SETCHECK, _display.transparent_bg ? BST_CHECKED : BST_UNCHECKED, NULL);
     SendMessage(GetDlgItem(hDlg, IDC_CHECK_CHAPTER_PAGE), BM_SETCHECK, _display.chapter_page ? BST_CHECKED : BST_UNCHECKED, NULL);
 }
 
diff --git a/Reader/Jsondata.cpp b/Reader/Jsondata.cpp
index 2407fec..1cd8327 100644
--- a/Reader/Jsondata.cpp
+++ b/Reader/Jsondata.cpp
@@ -600,6 +600,7 @@ class json_header_t
     cJSON* line_indent;
     cJSON* blank_lines;
     cJSON* chapter_page;
+    cJSON* transparent_bg;
     cJSON* ingore_version;
     cJSON* checkver_time;
     cJSON* global_key;
@@ -656,6 +657,7 @@ class json_header_t
         line_indent = cJSON_AddNumberToObject(parent, "line_indent", data->line_indent);
         blank_lines = cJSON_AddNumberToObject(parent, "blank_lines", data->blank_lines);
         chapter_page = cJSON_AddNumberToObject(parent, "chapter_page", data->chapter_page);
+        transparent_bg = cJSON_AddNumberToObject(parent, "transparent_bg", data->transparent_bg);
         ingore_version = cJSON_AddStringToObject(parent, "ingore_version", Utf16ToUtf8(data->ingore_version));
         checkver_time = cJSON_AddULongToObject(parent, "checkver_time", data->checkver_time);
 
@@ -779,6 +781,7 @@ class json_header_t
         line_indent = cJSON_GetObjectItem(parent, "line_indent");
         blank_lines = cJSON_GetObjectItem(parent, "blank_lines");
         chapter_page = cJSON_GetObjectItem(parent, "chapter_page");
+        transparent_bg = cJSON_GetObjectItem(parent, "transparent_bg");
         ingore_version = cJSON_GetObjectItem(parent, "ingore_version");
         checkver_time = cJSON_GetObjectItem(parent, "checkver_time");
 
@@ -966,6 +969,8 @@ class json_header_t
             data->blank_lines = blank_lines->valueint;
         if (chapter_page)
             data->chapter_page = chapter_page->valueint;
+        if (transparent_bg)
+            data->transparent_bg = transparent_bg->valueint;
         if (ingore_version)
             wcscpy(data->ingore_version, Utf8ToUtf16(ingore_version->valuestring));
         if (checkver_time)
diff --git a/Reader/Keyset.cpp b/Reader/Keyset.cpp
index 3c5a861..70e6a8c 100644
--- a/Reader/Keyset.cpp
+++ b/Reader/Keyset.cpp
@@ -19,6 +19,7 @@ extern LRESULT OnChapterUp(HWND, UINT, WPARAM, LPARAM);
 extern LRESULT OnChapterDown(HWND, UINT, WPARAM, LPARAM);
 extern LRESULT OnFontZoomIn(HWND, UINT, WPARAM, LPARAM);
 extern LRESULT OnFontZoomOut(HWND, UINT, WPARAM, LPARAM);
+extern LRESULT OnTransBG(HWND, UINT, WPARAM, LPARAM);
 extern int MessageBoxFmt_(HWND hWnd, UINT captionId, UINT uType, UINT formatId, ...);
 
 extern HINSTANCE hInst;
@@ -34,6 +35,9 @@ static BOOL _unregister_hotkey(HWND hWnd, DWORD kid);
 keydata_t g_Keysets[KI_MAXCOUNT] = 
 {
     { MAKELONG(KT_HOTKEY, KI_HIDE),             IDHK_SHWIN, 0, 0, MAKEWORD('H', HOTKEYF_ALT),                      IDC_HK_HIDE,        IDC_CHECK_HIDE,        OnHideWin,     IDS_HIDE_SHOW_WINDOW },
+    { MAKELONG(KT_HOTKEY, KI_HIDE2),            ID_HOTKEY_SHOW_HIDE_WINDOW2, 0, 0, MAKEWORD('H', HOTKEYF_CONTROL|HOTKEYF_ALT),   IDC_HK_HIDE2,       IDC_CHECK_HIDE2,       OnHideWin,     IDS_HIDE_SHOW_WINDOW },
+    { MAKELONG(KT_HOTKEY, KI_HIDE3),            ID_HOTKEY_SHOW_HIDE_WINDOW3, 0, 0, MAKEWORD('H', HOTKEYF_CONTROL|HOTKEYF_SHIFT), IDC_HK_HIDE3,       IDC_CHECK_HIDE3,       OnHideWin,     IDS_HIDE_SHOW_WINDOW },
+    { MAKELONG(KT_HOTKEY, KI_HIDE4),            ID_HOTKEY_SHOW_HIDE_WINDOW4, 0, 0, MAKEWORD('Q', HOTKEYF_ALT),                   IDC_HK_HIDE4,       IDC_CHECK_HIDE4,       OnHideWin,     IDS_HIDE_SHOW_WINDOW },
     { MAKELONG(KT_SHORTCUTKEY, KI_BORDER),      0,          0, 0, MAKEWORD(VK_F12, 0),                             IDC_HK_BORDER,      IDC_CHECK_BORDER,      OnHideBorder,  IDS_HIDE_SHOW_BORDER },
     { MAKELONG(KT_SHORTCUTKEY, KI_FULLSCREEN),  0,          0, 0, MAKEWORD(VK_F11, 0),                             IDC_HK_FULLSCREEN,  IDC_CHECK_FULLSCREEN,  OnFullScreen,  IDS_FULLSRCEEN },
     { MAKELONG(KT_SHORTCUTKEY, KI_TOP),         0,          0, 0, MAKEWORD('T', HOTKEYF_CONTROL),                  IDC_HK_TOP,         IDC_CHECK_TOP,         OnTopmost,     IDS_TOPMOST },
@@ -50,7 +54,8 @@ keydata_t g_Keysets[KI_MAXCOUNT] =
     { MAKELONG(KT_SHORTCUTKEY, KI_CHAPTERUP),   0,          0, 0, MAKEWORD(VK_LEFT, HOTKEYF_EXT|HOTKEYF_CONTROL),  IDC_HK_CHAPTERUP,   IDC_CHECK_CHAPTERUP,   OnChapterUp,   IDS_CHAPTER_UP },
     { MAKELONG(KT_SHORTCUTKEY, KI_CHAPTERDOWN), 0,          0, 0, MAKEWORD(VK_RIGHT, HOTKEYF_EXT|HOTKEYF_CONTROL), IDC_HK_CHAPTERDOWN, IDC_CHECK_CHAPTERDOWN, OnChapterDown, IDS_CHAPTER_DOWN },
     { MAKELONG(KT_SHORTCUTKEY, KI_FONTZOOMIN),  0,          0, 0, MAKEWORD(VK_OEM_PLUS, HOTKEYF_CONTROL),          IDC_HK_FONTZOOMIN,  IDC_CHECK_FONTZOOMIN,  OnFontZoomIn,  IDS_FONT_ZOOMIN },
-    { MAKELONG(KT_SHORTCUTKEY, KI_FONTZOOMOUT), 0,          0, 0, MAKEWORD(VK_OEM_MINUS, HOTKEYF_CONTROL),         IDC_HK_FONTZOOMOUT, IDC_CHECK_FONTZOOMOUT, OnFontZoomOut, IDS_FONT_ZOOMOUT }
+    { MAKELONG(KT_SHORTCUTKEY, KI_FONTZOOMOUT), 0,          0, 0, MAKEWORD(VK_OEM_MINUS, HOTKEYF_CONTROL),         IDC_HK_FONTZOOMOUT, IDC_CHECK_FONTZOOMOUT, OnFontZoomOut, IDS_FONT_ZOOMOUT },
+    { MAKELONG(KT_SHORTCUTKEY, KI_TRANS),       0,          0, 0, MAKEWORD(VK_F9, 0),                             IDC_HK_TRANS,       IDC_CHECK_TRANS,       OnTransBG,     IDS_TRANS_TOGGLE }
 };
 
 
@@ -65,31 +70,69 @@ void KS_Init(HWND hWnd, keyset_t *keyset)
     SetGlobalKey(hWnd);
 }
 
+// The config slot of an entry is the keyid stored in key (HIWORD), NOT its array
+// index in g_Keysets.  This decouples the table layout from the persisted config:
+// a new key can be inserted anywhere in g_Keysets without moving the slot of any
+// existing key, so configs written by older versions keep their meaning
+// (keyset[] is serialized positionally into JSON).
+static int _keyset_slot(const keydata_t *kd)
+{
+    int kid = (int)HIWORD(kd->key);
+
+    return (kid >= 0 && kid < MAX_KEYSET_COUNT) ? kid : -1;
+}
+
+// Which keys are enabled out of the box.  Everything else starts disabled and
+// is opt-in from the key settings dialog.
+static BOOL _default_enable(int kid)
+{
+    switch (kid)
+    {
+    case KI_HIDE:       // boss key 1 (Alt+H)
+    case KI_BORDER:     // hide/show border (F12)
+    case KI_PAGEUP:     // previous page (Left)
+    case KI_PAGEDOWN:   // next page (Right)
+    case KI_LINEUP:     // line up (Up)
+    case KI_LINEDOWN:   // line down (Down)
+        return TRUE;
+    default:
+        return FALSE;
+    }
+}
+
 void KS_UpdateKeyset(keyset_t *keyset)
 {
-    int i;
+    int i, kid;
 
     if (!keyset)
         return;
 
-    for (i=KI_HIDE; i<KI_MAXCOUNT && i<MAX_KEYSET_COUNT; i++)
+    for (i=KI_HIDE; i<KI_MAXCOUNT; i++)
     {
-        g_Keysets[i].pvalue =  &(keyset[i].value);
-        g_Keysets[i].is_disable = &(keyset[i].is_disable);
+        kid = _keyset_slot(&g_Keysets[i]);
+        if (kid < 0)
+            continue;
+
+        g_Keysets[i].pvalue     = &(keyset[kid].value);
+        g_Keysets[i].is_disable = &(keyset[kid].is_disable);
     }
 }
 
 void KS_GetDefaultKeyset(keyset_t *keyset)
 {
-    int i;
+    int i, kid;
 
     if (!keyset)
         return;
 
-    for (i=KI_HIDE; i<KI_MAXCOUNT && i<MAX_KEYSET_COUNT; i++)
+    for (i=KI_HIDE; i<KI_MAXCOUNT; i++)
     {
-        keyset[i].value = g_Keysets[i].defval;
-        keyset[i].is_disable = 0;
+        kid = _keyset_slot(&g_Keysets[i]);
+        if (kid < 0)
+            continue;
+
+        keyset[kid].value = g_Keysets[i].defval;
+        keyset[kid].is_disable = _default_enable(kid) ? 0 : 1;
     }
 }
 
@@ -101,6 +144,8 @@ void KS_OpenDlg(void)
 INT_PTR CALLBACK KS_DlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
 {
     int i,j;
+    int kid = 0;
+    BOOL enable = FALSE;
     LRESULT res;
     DWORD tempkeys[KI_MAXCOUNT] = {0};
     int tempable[KI_MAXCOUNT] = {0};
@@ -228,11 +273,18 @@ INT_PTR CALLBACK KS_DlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lPara
             return (INT_PTR)TRUE;
             break;
         case IDC_BUTTON_DEFAULT:
+            // Keep in sync with KS_GetDefaultKeyset: restore the default values and
+            // check/enable only the keys that are enabled by default.
             for (i=KI_HIDE; i<KI_MAXCOUNT; i++)
             {
+                kid = _keyset_slot(&g_Keysets[i]);
+                if (kid < 0)
+                    continue;
+
+                enable = _default_enable(kid);
                 SendMessage(GetDlgItem(hDlg, g_Keysets[i].ctrl_id), HKM_SETHOTKEY, g_Keysets[i].defval, 0);
-                SendMessage(GetDlgItem(hDlg, g_Keysets[i].able_id), BM_SETCHECK, BST_CHECKED, NULL);
-                EnableWindow(GetDlgItem(hDlg, g_Keysets[i].ctrl_id), TRUE);
+                SendMessage(GetDlgItem(hDlg, g_Keysets[i].able_id), BM_SETCHECK, enable ? BST_CHECKED : BST_UNCHECKED, NULL);
+                EnableWindow(GetDlgItem(hDlg, g_Keysets[i].ctrl_id), enable);
             }
             break;
         default:
@@ -380,21 +432,23 @@ static BOOL _unregister_hotkey(HWND hWnd, DWORD kid)
 
 BOOL KS_RegisterAllHotKey(HWND hWnd)
 {
-    int i;
+    int i, fail = 0;
     TCHAR desc[256] = { 0 };
 
     for (i=KI_HIDE; i<KI_MAXCOUNT; i++)
     {
         if (LOWORD(g_Keysets[i].key) == KT_HOTKEY)
         {
+            if (g_Keysets[i].is_disable && *(g_Keysets[i].is_disable))
+                continue;
             LoadString(hInst, g_Keysets[i].desc, desc, 256);
             if (!_register_hotkey(hWnd, g_Keysets[i].key_id, *(g_Keysets[i].pvalue), desc))
             {
-                return FALSE;
+                fail++;   // do not abort: other hot keys must still register
             }
         }
     }
-    return TRUE;
+    return (fail == 0);
 }
 
 BOOL KS_UnRegisterAllHotKey(HWND hWnd)
diff --git a/Reader/Keyset.h b/Reader/Keyset.h
index d862f13..ac52a6f 100644
--- a/Reader/Keyset.h
+++ b/Reader/Keyset.h
@@ -29,6 +29,10 @@ typedef enum keyid_t
     KI_CHAPTERDOWN,
     KI_FONTZOOMIN,
     KI_FONTZOOMOUT,
+    KI_HIDE2,       // boss key 2 (config slot comes from keyid, so its position here keeps old configs valid)
+    KI_HIDE3,       // boss key 3
+    KI_HIDE4,       // boss key 4
+    KI_TRANS,       // toggle transparent background (config slot comes from keyid, so appending keeps old configs valid)
     KI_MAXCOUNT
 } keyid_t;
 
diff --git a/Reader/Reader.cpp b/Reader/Reader.cpp
index c995807..87e4bfd 100644
--- a/Reader/Reader.cpp
+++ b/Reader/Reader.cpp
@@ -1830,6 +1830,12 @@ LRESULT OnCreate(HWND hWnd)
     _WndInfo.bTopMost = (_header->exstyle & WS_EX_TOPMOST) == WS_EX_TOPMOST;
     _WndInfo.status = (_header->style & WS_MINIMIZEBOX) == 0 ? ds_fullscreen : (((_header->style & WS_CAPTION) == 0) ? ds_borderless : ds_normal);
 
+    // Borderless mode removes the menu bar, so the "hide/show border" key is the only
+    // way back to it.  Never run without that escape hatch (e.g. after hand-editing the
+    // config), otherwise the menu would be unreachable for good.
+    if (_WndInfo.status == ds_borderless && _header->keyset[KI_BORDER].is_disable)
+        _header->keyset[KI_BORDER].is_disable = 0;
+
     _WndInfo.hMenu = GetMenu(hWnd);
     // create status bar
     _WndInfo.hStatusBar = CreateStatusWindow(WS_CHILD | WS_VISIBLE, _T("Please open a text."), hWnd, IDC_STATUSBAR);
@@ -2191,6 +2197,13 @@ VOID OnDraw(HWND hWnd)
     {
         alpha = _header->alpha < MIN_ALPHA_VALUE ? MIN_ALPHA_VALUE : _header->alpha;
     }
+    else if (_header->transparent_bg)
+    {
+        // Transparent background: alpha 0 makes the desktop show through and
+        // UpdateLayeredWindow turns those pixels click-through.  The text is
+        // composited separately with _textAlpha, so it stays opaque.
+        alpha = 0;
+    }
 
     // load bg image
     image = LoadBGImage(w, h, alpha);
@@ -2505,6 +2518,15 @@ LRESULT OnTopmost(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
     return 0;
 }
 
+// Toggle the transparent-background flag.  The visual effect only shows in
+// borderless mode (F12), matching the display-settings checkbox behaviour.
+LRESULT OnTransBG(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
+{
+    _header->transparent_bg = !_header->transparent_bg;
+    Invalidate(hWnd, TRUE, FALSE);
+    return 0;
+}
+
 LRESULT OnOpenFile(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
 {
     if (IsWindow(_hFindDlg))
diff --git a/Reader/Reader.h b/Reader/Reader.h
index 7bbcb74..f1f2be7 100644
--- a/Reader/Reader.h
+++ b/Reader/Reader.h
@@ -78,6 +78,7 @@ LRESULT             OnSize(HWND, UINT, WPARAM, LPARAM);
 // WM_KEYWORD begin
 LRESULT             OnHideWin(HWND, UINT, WPARAM, LPARAM);
 LRESULT             OnHideBorder(HWND, UINT, WPARAM, LPARAM);
+LRESULT             OnTransBG(HWND, UINT, WPARAM, LPARAM);
 LRESULT             OnFullScreen(HWND, UINT, WPARAM, LPARAM);
 LRESULT             OnTopmost(HWND, UINT, WPARAM, LPARAM);
 LRESULT             OnOpenFile(HWND, UINT, WPARAM, LPARAM);
diff --git a/Reader/Reader_zh-cn.rc b/Reader/Reader_zh-cn.rc
index 2b3ec6d..327591a 100644
Binary files a/Reader/Reader_zh-cn.rc and b/Reader/Reader_zh-cn.rc differ
diff --git a/Reader/resource.h b/Reader/resource.h
index d364e4e..ad772b2 100644
Binary files a/Reader/resource.h and b/Reader/resource.h differ
diff --git a/Reader/types.h b/Reader/types.h
index 7faf5cb..b274242 100644
--- a/Reader/types.h
+++ b/Reader/types.h
@@ -63,6 +63,12 @@
 
 
 #define ID_HOTKEY_SHOW_HIDE_WINDOW  100
+
+#define ID_HOTKEY_SHOW_HIDE_WINDOW2 200    // RegisterHotKey id: boss key 2
+#define ID_HOTKEY_SHOW_HIDE_WINDOW3 201    // RegisterHotKey id: boss key 3
+#define ID_HOTKEY_SHOW_HIDE_WINDOW4 202    // RegisterHotKey id: boss key 4
+#define MAX_BOSS_KEY                4      // boss key count
+
 #define IDT_TIMER_PAGE              102
 #ifdef ENABLE_NETWORK
 #define IDT_TIMER_UPGRADE           103
@@ -203,6 +209,7 @@ typedef struct header_t
     int use_same_font;
     u32 bg_color;
     BYTE alpha;
+    int transparent_bg;   // 1 = background fully transparent, text stays opaque
     int char_gap;
     int line_gap;
     int paragraph_gap;