Highcharts: Context Button menu hidden with several small charts

I’m using Highcharts to create several charts with a small height size.

Every chart need to have a context button with several options, but the menu always get hidden by the chart below.

I already search and try many solutions:

HighCharts: context menu hidden for small charts

http://javascript.wekeepcoding.com/article/13901234/Table+appearing+in+front+of+my+dropdown+menu

But the problem is, however the menu comes to front, when hits another context menu is impossible to click in the options.

JS:

contextButton: {
        align: "left",
        _titleKey: "preferencesKey", 
        symbolSize: 12,
        theme: {
          fill: null
        },
        menuItems: [
          {
            text: "Add Chart",
            onclick: function() {
              addAddButtons();
            }
          },
          {
            text: "Preferences",
            onclick: function() {
              addPreferencesButtons(chart);
              console.log(chart);
            }
          },
          {
            text: "Remove Chart",
            onclick: function() {
              addRemoveButtons(chart);
            }
          }

CSS:

 .highcharts-container{
      overflow: visible;
      z-index: 1;
    }

I’m working in Electron. I don’t know why but the recomendation of highcharts documentation to use .highcharts contextbutton doesn’t work.

Anyone knows how to make this work?
Thanks.