Agrega estilo al header de la seccion

ContactsApp/Base.lproj/Main.storyboard

@@ -19,16 +19,8 @@
                                 <rect key="frame" x="0.0" y="44" width="375" height="623"/>
                                 <color key="backgroundColor" systemColor="systemBackgroundColor" cocoaTouchSystemColor="whiteColor"/>
                                 <prototypes>
-                                    <tableViewCell clipsSubviews="YES" contentMode="scaleToFill" preservesSuperviewLayoutMargins="YES" selectionStyle="default" indentationWidth="10" id="l8U-st-Wic">
-                                        <rect key="frame" x="0.0" y="28" width="375" height="43.5"/>
-                                        <autoresizingMask key="autoresizingMask"/>
-                                        <tableViewCellContentView key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" preservesSuperviewLayoutMargins="YES" insetsLayoutMarginsFromSafeArea="NO" tableViewCell="l8U-st-Wic" id="FAe-5V-uSO">
-                                            <rect key="frame" x="0.0" y="0.0" width="375" height="43.5"/>
-                                            <autoresizingMask key="autoresizingMask"/>
-                                        </tableViewCellContentView>
-                                    </tableViewCell>
                                     <tableViewCell clipsSubviews="YES" contentMode="scaleToFill" preservesSuperviewLayoutMargins="YES" selectionStyle="default" indentationWidth="10" reuseIdentifier="contactName" id="QkB-8k-kbX">
-                                        <rect key="frame" x="0.0" y="71.5" width="375" height="43.5"/>
+                                        <rect key="frame" x="0.0" y="28" width="375" height="43.5"/>
                                         <autoresizingMask key="autoresizingMask"/>
                                         <tableViewCellContentView key="contentView" opaque="NO" clipsSubviews="YES" multipleTouchEnabled="YES" contentMode="center" preservesSuperviewLayoutMargins="YES" insetsLayoutMarginsFromSafeArea="NO" tableViewCell="QkB-8k-kbX" id="AMU-de-w3M">
                                             <rect key="frame" x="0.0" y="0.0" width="375" height="43.5"/>
@@ -59,7 +51,7 @@
                 </viewController>
                 <placeholder placeholderIdentifier="IBFirstResponder" id="On8-yo-4E7" userLabel="First Responder" customClass="UIResponder" sceneMemberID="firstResponder"/>
             </objects>
-            <point key="canvasLocation" x="1414.4927536231885" y="63.616071428571423"/>
+            <point key="canvasLocation" x="1413.5999999999999" y="63.418290854572717"/>
         </scene>
         <!--Single Contact View Controller-->
         <scene sceneID="wAp-rN-Dr5">

ContactsApp/ContactSection.xib

@@ -27,7 +27,7 @@
                     <nil key="highlightedColor"/>
                 </label>
             </subviews>
-            <color key="backgroundColor" red="0.90924546632124348" green="0.90924546632124348" blue="0.90924546632124348" alpha="0.59999999999999998" colorSpace="custom" customColorSpace="sRGB"/>
+            <color key="backgroundColor" cocoaTouchSystemColor="lightTextColor"/>
             <constraints>
                 <constraint firstItem="vUN-kp-3ea" firstAttribute="bottom" secondItem="2Vg-Y7-9zD" secondAttribute="bottom" constant="1" id="M1Z-qU-8CJ"/>
                 <constraint firstItem="rgh-bc-PuT" firstAttribute="leading" secondItem="vUN-kp-3ea" secondAttribute="leading" constant="16" id="PMm-R4-l0c"/>

ContactsApp/ContactSectionView.swift

@@ -8,14 +8,8 @@
 
 import UIKit
 
-class ContactSectionView: UIView {
+class ContactSectionView: UITableViewHeaderFooterView {
 
     @IBOutlet weak var labelLetter: UILabel!
     @IBOutlet weak var labelExpandable: UIButton!
-    
-    override func draw(_ rect: CGRect) {
-        super .draw(rect)
-        //title.text = "Jahata"
-    }
-
 }

ContactsApp/ContactsViewController.swift

@@ -18,6 +18,7 @@ class ContactsViewController: UIViewController {
     
     override func viewDidLoad() {
         super.viewDidLoad()
+        contactsTable.register(UINib(nibName: "ContactSection", bundle: nil), forHeaderFooterViewReuseIdentifier: "headerId")
         importContacts()
         contactsTable.tableFooterView = UIView(frame: .zero)
     }
@@ -110,14 +111,15 @@ extension ContactsViewController: UITableViewDelegate, UITableViewDataSource {
     }
     
     func tableView(_ tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
-        let button = UIButton(type: .system)
-        button.setTitle("Λ", for: .normal)
-        button.setTitleColor(.black, for: .normal)
-        button.titleLabel?.font = UIFont.boldSystemFont(ofSize: 15)
-        button.backgroundColor = .systemGray4
-        button.addTarget(self, action: #selector(interactSection), for: .touchUpInside)
-        button.tag = section
-        return button//ʌΛ
+        let header = contactsTable.dequeueReusableHeaderFooterView(withIdentifier: "headerId") as! ContactSectionView
+        header.contentView.backgroundColor = .systemGray4
+        header.labelExpandable.setTitle("Λ", for: .normal)
+        header.labelExpandable.setTitleColor(.black, for: .normal)
+        header.labelExpandable.titleLabel?.font = UIFont.boldSystemFont(ofSize: 15)
+        header.labelExpandable.addTarget(self, action: #selector(interactSection), for: .touchUpInside)
+        header.labelExpandable.tag = section
+        header.labelLetter.text = contactStructArray[section].letter
+        return header//ʌΛ
     }
     
     @objc func interactSection(button : UIButton) {