Pulsante nella barra dei TAB

Like this?

With dialog when you click on ?

You can try this code in Ninox + NativeJS :

#{// put your action in this function }#;
function doSomeThing( title : text, body : text ) do
    var res := dialog(title, body, ["modify", "save"]);
    switch res do
        case "modify" : alert("modify...")
        case "save" : alert("save...")
    end;
end;

#{:text
// On first time, create the container and the button
if (!ui.myContainer) {
    ui.myContainer = document.createElement('div');
    ui.myButton = document.createElement('button');
    // add the bonton in the container
    ui.myContainer.append(ui.myButton);
    // add the container in the menu bar.
    ui.$menuRight[0].insertBefore(ui.myContainer,ui.$menuRight[0].children[0]);
}

// button initialization
ui.myButton.innerText = 'Azioni';
// call the doSomeThing function when the button is clicked
ui.myButton.onclick = (event) => {doSomeThing( 'my title', 'what do you whant to do ?')};

}#

I had misread your document about the position of the button. I changed the code in this sense. Now the container is a child of the tab bar and not of the right menu.

warning : this code must be executed when the form is displayed, not before.

#{// put your action in this function }#;
function doSomeThing( title : text, body : text ) do
    var res := dialog(title, body, ["modify", "save"]);
    switch res do
        case "modify" : alert("modify...")
        case "save" : alert("save...")
    end;
end;

#{:text

// find the tab bar of top level form.
 var tabs = (widgets.popupEditorStack.length > 0 ? widgets.popupEditorStack[widgets.popupEditorStack.length - 1] : ui.sideEditor && ui.sideEditor).tabsEl[0];

// if it's first time, create the container and the button
if (!tabs.myContainer) {
    tabs.myContainer = document.createElement('div');
    tabs.myButton = document.createElement('div');
    // add the bonton in the container
    tabs.myContainer.append(tabs.myButton);

    // add the current container in the tab bar.
    tabs.append(tabs.myContainer);
}

// container aspect initialization
tabs.myContainer.className = 'tab';
tabs.myContainer.style.float = 'inline-end';
tabs.myContainer.style.backgroundColor = '#3059f0';
tabs.myContainer.style.color = 'white';
tabs.myContainer.style.width = '100px';
    // button aspect initialization
tabs.myButton.innerText = 'Azioni';
tabs.myButton.style.textAlign = 'center';  // call the doSomeThing function when the button is clicked
tabs.myButton.onclick = (event) => {doSomeThing( 'my title', 'what do you whant to do ?')};  }#

To change the size of the button, you have to change the style of the container or the button itself. The same goes for the color and all other aspect attributes. Use the "style" property of the elements for this : https://developer.mozilla.org/en-US/docs/Web/API/CSS_Object_Model/Using_dynamic_styling_information