diff --git a/CustomKeyboard/View/KBKeyBoardMainView.m b/CustomKeyboard/View/KBKeyBoardMainView.m
index 40acc9c..0c5dff5 100644
--- a/CustomKeyboard/View/KBKeyBoardMainView.m
+++ b/CustomKeyboard/View/KBKeyBoardMainView.m
@@ -39,7 +39,8 @@
         [self addSubview:self.keyboardView];
         [self.keyboardView mas_makeConstraints:^(MASConstraintMaker *make) {
             make.left.right.equalTo(self);
-            make.top.equalTo(self.topBar.mas_bottom).offset(4);
+//            make.top.equalTo(self.topBar.mas_bottom).offset(4);
+            make.height.mas_equalTo(200);
             make.bottom.equalTo(self.mas_bottom).offset(-4);
         }];
         
diff --git a/CustomKeyboard/View/KBKeyboardView.m b/CustomKeyboard/View/KBKeyboardView.m
index 50dbedb..9ffe4f8 100644
--- a/CustomKeyboard/View/KBKeyboardView.m
+++ b/CustomKeyboard/View/KBKeyboardView.m
@@ -54,7 +54,7 @@
     [self.row1 mas_makeConstraints:^(MASConstraintMaker *make) {
         make.top.equalTo(self.mas_top).offset(8);
         make.left.right.equalTo(self);
-        make.height.mas_equalTo(44);
+        make.height.mas_equalTo(40);
     }];
     [self.row2 mas_makeConstraints:^(MASConstraintMaker *make) {
         make.top.equalTo(self.row1.mas_bottom).offset(vSpacing);
@@ -276,6 +276,10 @@
 }
 
 - (void)buildRow:(UIView *)row withKeys:(NSArray<KBKey *> *)keys edgeSpacerMultiplier:(CGFloat)edgeSpacerMultiplier {
+    // 第 4 行（底部控制行）使用单独的布局规则：
+    // 123/ABC、AI、Send 给定尺寸，Space 自动吃掉剩余宽度。
+    BOOL isBottomControlRow = [self kb_isBottomControlRowWithKeys:keys];
+
     CGFloat hInset = 6;   // 行左右内边距
     CGFloat spacing = 0;  // 键与键之间的间距
     UIView *previous = nil;
@@ -352,6 +356,7 @@
 
         previous = btn;
     }
+
     // 右侧使用内边距或右占位
     [previous mas_makeConstraints:^(MASConstraintMaker *make) {
         if (rightSpacer) {
@@ -361,6 +366,13 @@
         }
     }];
 
+    // 底部控制行：在第一轮已完成左右约束的前提下，仅给 123/ABC、AI、Send 指定宽度，
+    // Space 不加宽度约束，让其自动填充剩余空间。
+    if (isBottomControlRow) {
+        [self kb_applyBottomControlRowWidthInRow:row];
+        return;
+    }
+
     // 第二遍：以首个字符键为基准，统一设置特殊键宽度倍数
     KBKeyButton *firstChar = nil;
     BOOL hasCharacterInRow = NO;
@@ -402,6 +414,7 @@
             // 一类键强制宽高比 1:1：
             // - 第三行：Shift、Backspace
             // - 第四行：123/ABC（ModeChange）、#+=（SymbolsToggle）、AI（Custom）
+            //   （真正的底部控制行在上面已单独处理，这里主要服务于第三行的 #+= 等）
             BOOL isBottomModeKey = (b.key.type == KBKeyTypeModeChange) ||
                                    (b.key.type == KBKeyTypeSymbolsToggle) ||
                                    (b.key.type == KBKeyTypeCustom);
@@ -409,7 +422,7 @@
                 b.key.type == KBKeyTypeBackspace ||
                 isBottomModeKey) {
                 [b mas_makeConstraints:^(MASConstraintMaker *make) {
-                    make.width.equalTo(b.mas_height); // 宽度 = 高度，做成正方形
+                    make.width.equalTo(b.mas_height).multipliedBy(1.2); // 宽度 = 高度，做成正方形
                 }];
                 continue;
             }
@@ -445,6 +458,79 @@
     }
 }
 
+#pragma mark - Row Helpers (Bottom Control Row)
+
+// 判断是否为底部控制行：包含 Space + Return，且有 ModeChange/SymbolsToggle，
+// 并且不再含字符键。
+- (BOOL)kb_isBottomControlRowWithKeys:(NSArray<KBKey *> *)keys {
+    BOOL hasSpace = NO;
+    BOOL hasReturn = NO;
+    BOOL hasModeOrSymbols = NO;
+    for (KBKey *k in keys) {
+        if (k.type == KBKeyTypeCharacter) {
+            return NO;
+        }
+        if (k.type == KBKeyTypeSpace) {
+            hasSpace = YES;
+        } else if (k.type == KBKeyTypeReturn) {
+            hasReturn = YES;
+        } else if (k.type == KBKeyTypeModeChange || k.type == KBKeyTypeSymbolsToggle) {
+            hasModeOrSymbols = YES;
+        }
+    }
+    return hasSpace && hasReturn && hasModeOrSymbols;
+}
+
+// 为底部控制行设置宽度：
+// - 123/ABC、AI：正方形（宽 = 行高）
+// - Send：宽 = 模式键宽度的 2.4 倍
+// - Space：不加宽度约束，依靠左右约束自动填充剩余空间。
+- (void)kb_applyBottomControlRowWidthInRow:(UIView *)row {
+    KBKeyButton *modeBtn = nil;
+    KBKeyButton *aiBtn = nil;
+    KBKeyButton *spaceBtn = nil;
+    KBKeyButton *retBtn = nil;
+
+    for (UIView *v in row.subviews) {
+        if (![v isKindOfClass:[KBKeyButton class]]) continue;
+        KBKeyButton *b = (KBKeyButton *)v;
+        switch (b.key.type) {
+            case KBKeyTypeModeChange:
+            case KBKeyTypeSymbolsToggle:
+                modeBtn = b;
+                break;
+            case KBKeyTypeCustom:
+                aiBtn = b;
+                break;
+            case KBKeyTypeSpace:
+                spaceBtn = b;
+                break;
+            case KBKeyTypeReturn:
+                retBtn = b;
+                break;
+            default:
+                break;
+        }
+    }
+
+    if (!modeBtn || !aiBtn || !spaceBtn || !retBtn) {
+        return;
+    }
+
+    // 行高由外部约束为固定值（等于 row1 高度），这里用行高作为“正方形”的边长。
+    [modeBtn mas_makeConstraints:^(MASConstraintMaker *make) {
+        make.width.equalTo(row.mas_height).multipliedBy(1.2);
+    }];
+    [aiBtn mas_makeConstraints:^(MASConstraintMaker *make) {
+        make.width.equalTo(row.mas_height).multipliedBy(1.2);
+    }];
+    [retBtn mas_makeConstraints:^(MASConstraintMaker *make) {
+        // Send 按钮：宽度为模式键的 2.4 倍
+        make.width.equalTo(modeBtn.mas_width).multipliedBy(2);
+    }];
+    // Space 不设置宽度；通过此前已建立的左右约束自动占满剩余宽度。
+}
+
 #pragma mark - Actions
 
 - (void)onKeyTapped:(KBKeyButton *)sender {
@@ -485,7 +571,7 @@
     CGFloat centerX = CGRectGetMidX(btnFrameInSelf);
     CGFloat centerY = CGRectGetMinY(btnFrameInSelf) - previewHeight * 0.6;
 
-    self.previewView.frame = CGRectMake(0, 0, previewWidth, previewHeight);
+    self.previewView.frame = CGRectMake(0, 0, 40, previewHeight);
     self.previewView.center = CGPointMake(centerX, centerY);
     self.previewView.alpha = 0.0;
     self.previewView.hidden = NO;