Avoid explicit color definitions in Qt Quick GUI

Those might break dark mode and using custom color palettes in general.

qml/EntriesPage.qml

@@ -50,9 +50,6 @@ Kirigami.ScrollablePage {
             shortcut: "Ctrl+Shift+A"
         }
     ]
-    background: Rectangle {
-        color: Kirigami.Theme.backgroundColor
-    }
 
     // dialog to confirm deletion of an entry
     BasicDialog {

qml/FieldsDelegate.qml

@@ -40,7 +40,6 @@ Item {
                             }
                             return pieces.join(": ")
                         }
-                        color: palette.text
                         verticalAlignment: Text.AlignVCenter
                     }
                 }

qml/FieldsPage.qml

@@ -25,9 +25,6 @@ Kirigami.ScrollablePage {
             shortcut: "Ctrl+Shift+A"
         }
     ]
-    background: Rectangle {
-        color: Kirigami.Theme.backgroundColor
-    }
 
     // dialog to edit certain field
     BasicDialog {

qml/PasswordDialog.qml

@@ -44,11 +44,6 @@ BasicDialog {
             placeholderText: newPassword
                 ? qsTr("enter password here, leave empty for no encryption")
                 : qsTr("enter password here")
-            color: "#101010"
-            placeholderTextColor: "#505050"
-            background: Rectangle {
-                border.color: "#5d5e6d"
-            }
             Keys.onPressed: (event) => passwordDialog.acceptOnReturn(event)
         }
         Controls.TextField {
@@ -58,11 +53,6 @@ BasicDialog {
             enabled: visible && !showCharactersCheckBox.checked
             echoMode: TextInput.Password
             placeholderText: qsTr("repeat password")
-            color: "#101010"
-            placeholderTextColor: "#505050"
-            background: Rectangle {
-                border.color: passwordDialog.canAccept ? "#089900" : "#ff0000"
-            }
             Keys.onPressed: passwordDialog.acceptOnReturn(event)
         }
         Controls.CheckBox {