Black on grey without border in light mode (#492)

follow-up to #489, implementing
#489 (comment)


### light
![light - sign
in](https://github.com/user-attachments/assets/96600ddf-06a3-46c7-b8bf-78d148bb58bd)


### dark
![dark - sign
in](https://github.com/user-attachments/assets/7354983e-690d-492e-a477-ab71d1f9eac8)

BeeKit/UI/BSButton.swift

@@ -12,15 +12,7 @@ import UIKit
 public class BSButton : UIButton {
 
     required init?(coder aDecoder: NSCoder) {
-        super.init(coder: aDecoder)
-
-        registerForTraitChanges(
-            [UITraitUserInterfaceStyle.self]) {
-                (self: Self, previousTraitCollection: UITraitCollection) in
-                self.resetStyle()
-            }
-
-        self.setUp()
+        fatalError("init(coder:) has not been implemented; neither xib nor storyboards in use")
     }
 
     override init(frame: CGRect) {
@@ -32,23 +24,22 @@ public class BSButton : UIButton {
                 self.resetStyle()
             }
 
-        self.setUp()
+        self.resetStyle()
     }
 
-    private func setUp() {
+    private func resetStyle() {
+        self.configuration = .filled()
+
         self.titleLabel?.font = UIFont.beeminder.defaultBoldFont
+
         self.setTitleColor(dynamicTitleColor, for: UIControl.State())
         self.tintColor = dynamicTintFillColor
-        self.configuration = .filled()
+
+        self.backgroundColor = .clear
 
-        self.layer.borderColor = UIColor.Beeminder.yellow.cgColor
-        self.layer.borderWidth = 1
-        self.layer.cornerRadius = 4
-    }
-
-    private func resetStyle() {
-        self.tintColor = dynamicTintFillColor
-        self.setTitleColor(dynamicTitleColor, for: UIControl.State())
+        self.layer.borderColor = traitCollection.userInterfaceStyle == .dark ? UIColor.Beeminder.yellow.cgColor : UIColor.clear.cgColor
+        self.layer.borderWidth = traitCollection.userInterfaceStyle == .dark ? 1 : 0
+        self.layer.cornerRadius = traitCollection.userInterfaceStyle == .dark ? 4 : 0
     }
 
     private let dynamicTintFillColor = UIColor { traitCollection in