created and completed the edit-user.fxml, css and the controller

client/app/src/main/java/users/EditUserController.java

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+package users;
+
+import javafx.event.ActionEvent;
+import javafx.fxml.FXML;
+import javafx.scene.Node;
+import javafx.scene.control.Label;
+import javafx.scene.control.TextField;
+import javafx.scene.control.ToggleButton;
+import javafx.scene.paint.Paint;
+import javafx.stage.Stage;
+import java.util.Objects;
+
+public class EditUserController {
+
+    public TextField textName;
+    public TextField textPassword;
+    public TextField textPasswordSecond;
+    public ToggleButton checkButtonIsAdmin;
+    public TextField textLogin;
+    public TextField textForename;
+    public Label labelError;
+
+    @FXML
+    public void saveUser(ActionEvent event) {
+        labelError.setTextFill(Paint.valueOf("Red"));
+        if (textLogin.getText().trim().isEmpty()){
+            labelError.setText("Bitte Login Namen angeben");
+            return;
+        }
+        if (textForename.getText().trim().isEmpty()) {
+            labelError.setText("Bitte Vornamen eingeben!");
+            return;
+        }
+        if (textName.getText().trim().isEmpty()) {
+            labelError.setText("Bitte Nachnamen eingeben!");
+            return;
+        }
+        if (textPassword.getText().trim().isEmpty()) {
+            labelError.setText("Bitte Passwort eingeben!");
+            return;
+        }
+        if (!Objects.equals(textPassword.getText(), textPasswordSecond.getText())){
+            labelError.setText("Passwörter stimmen nicht überein!");
+            return;
+        }
+
+        Stage stage = (Stage) ((Node) event.getSource()).getScene().getWindow();
+        stage.close();
+    }
+
+    @FXML
+    public void abortBtnClick(ActionEvent event) {
+        Stage stage = (Stage) ((Node) event.getSource()).getScene().getWindow();
+        stage.close();
+    }
+}

client/app/src/main/resources/users/edit-user.css

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+* {
+   -fx-base-background-color: #2B2D42;
+   -fx-base1-background-color: #525E74;
+
+   -fx-main-border-color: #B0B0B0;
+   -fx-main-text-color: #ffffff;
+}
+
+
+GridPane{
+    -fx-background-color: #3E415F;
+    -fx-padding: 20px;
+    -fx-font-size: 20px;
+    -fx-font-family: Segoe UI;
+
+    -fx-border-insets: 1;
+    -fx-border-color: #B0B0B0;
+    -fx-border-style: solid;
+    -fx-border-width: 2;
+    -fx-effect: dropshadow(three-pass-box, rgba(100, 100, 100, 1), 24, 0.5, 0, 0);
+}
+
+.mainLabel{
+    -fx-padding: 10px;
+    -fx-max-width: 400px;
+    -fx-min-width: 400px;
+    -fx-font-weight: bold;
+    -fx-alignment: top-center;
+}
+
+
+Label{
+    -fx-text-fill: white;
+    -fx-max-width: 150px;
+    -fx-min-width: 150px;
+}
+
+.textField{
+    -fx-max-width: 400px;
+    -fx-min-width: 400px;
+}
+
+.errorMessage{
+    -fx-font-weight: bold;
+    -fx-max-width: 200px;
+    -fx-text-fill: #ff5555;
+    -fx-font-size: 16px;
+    -fx-max-width: 400px;
+    -fx-min-width: 400px;
+}
+
+Button{
+    -fx-max-width: 150px;
+    -fx-min-width: 150px;
+}
+
+.btnLogin{
+    -fx-font-weight: bold;
+}

client/app/src/main/resources/users/edit-user.fxml

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+<?xml version="1.0" encoding="UTF-8"?>
+
+<?import javafx.scene.control.*?>
+<?import javafx.scene.layout.*?>
+<?import javafx.geometry.Insets?>
+<GridPane xmlns="http://javafx.com/javafx"
+          xmlns:fx="http://javafx.com/fxml"
+          fx:controller="users.EditUserController">
+    <columnConstraints>
+        <ColumnConstraints minWidth="100"/>
+        <ColumnConstraints minWidth="100"/>
+        <ColumnConstraints minWidth="100"/>
+    </columnConstraints>
+    <rowConstraints>
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+        <RowConstraints vgrow="ALWAYS" />
+    </rowConstraints>
+
+    <Label styleClass="mainLabel" GridPane.columnIndex="2" >User Bearbeiten</Label>
+
+    <Label styleClass="inputLabel" GridPane.rowIndex="1" GridPane.columnIndex="1">Login:</Label>
+    <Label styleClass="inputLabel" GridPane.rowIndex="2" GridPane.columnIndex="1">Vorname:</Label>
+    <Label styleClass="inputLabel" GridPane.rowIndex="3" GridPane.columnIndex="1">Nachname:</Label>
+    <Label styleClass="inputLabel" GridPane.rowIndex="4" GridPane.columnIndex="1">Passwort:</Label>
+    <Label styleClass="inputLabel" GridPane.rowIndex="5" GridPane.columnIndex="1">Passwort wiederholen:</Label>
+
+    <Label styleClass="inputLabelAdmin" GridPane.rowIndex="6" GridPane.columnIndex="1">Admin:</Label>
+
+    <TextField fx:id="textLogin" styleClass="textField" GridPane.columnIndex="2" GridPane.rowIndex="1" />
+    <TextField fx:id="textForename" styleClass="textField" GridPane.columnIndex="2" GridPane.rowIndex="2" />
+    <TextField fx:id="textName" styleClass="textField" GridPane.columnIndex="2" GridPane.rowIndex="3" />
+    <TextField fx:id="textPassword" styleClass="textField" GridPane.columnIndex="2" GridPane.rowIndex="4" />
+    <TextField fx:id="textPasswordSecond" styleClass="textField" GridPane.columnIndex="2" GridPane.rowIndex="5" />
+
+    <ToggleButton fx:id="checkButtonIsAdmin" GridPane.columnIndex="2" GridPane.rowIndex="6"/>
+
+    <Label fx:id="labelError" styleClass="errorMessage" GridPane.columnIndex="2" GridPane.rowIndex="7"/>
+
+    <HBox GridPane.columnIndex="2" GridPane.rowIndex="8" alignment="CENTER_RIGHT">
+        <HBox.margin>
+            <Insets right="100" left="100"/>
+        </HBox.margin>
+        <Button onAction="#abortBtnClick">Abbrechen</Button>
+        <Button onAction="#saveUser" styleClass="btnLogin" >Speichern</Button>
+
+    </HBox>
+</GridPane>