Javascript – Using Highcharts to create an items chart (aka "waffle" chart) – how to I control padding?

I am using Highcharts to create a waffle chart. Here’s a good example:

https://datavizproject.com/data-type/percentage-grid/

Highcharts calls them "item charts", and they work pretty well.

However, I can’t figure out how to control the spacing/padding between the items.

I’ve tried using the itemPadding property, but that only seems to set the padding between the rows, but not the columns.

Here’s a working fiddle:

https://jsfiddle.net/stuehler/frt80u2p/4/

As you can see in this screenshot below, the row padding is 1px (itemPadding: 1 – that’s what I want), but the column padding is much larger:

Here is the code I’m using:

Highcharts.chart('container', {

  chart: {
    type: 'item'
  },

  series: [{
    marker: {
      symbol: 'square'
    },
    itemPadding: 1,
    rows: 10,
    data: [
      {
        name: 'Male',
        y: 43
      },
      {
        name: 'Female',
        y: 57
      }
    ]
  }]
});

Thanks in advance for your help!