Highcharts Heatmap issue behind title text with alternateGridColor when using setOptions
<p>I'm having an issue when using setOptions with Highcharts heatmaps.
Using highcharts' own example fiddle, adding some code to set the alternate grid colour causes the colour to appear behind the title text;</p>

<p><a href="https://i.stack.imgur.com/XiBLp.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XiBLp.jpg" alt="Heat map alternateGridColor title issue"></a></p>

<pre><code>Highcharts.theme = {
    yAxis: {
        alternateGridColor: '#EEEEEE'
    }
};

// Apply the theme
var HighchartsOptions = Highcharts.setOptions(Highcharts.theme);
</code></pre>

<p><a href="http://jsfiddle.net/mattscotty/m56z3gtt/1/" rel="nofollow noreferrer">http://jsfiddle.net/mattscotty/m56z3gtt/1/</a></p>

<p>This issue does not occur when setting the colour in the chart settings directly and overriding the colour in the chart settings, does not remove or override the issue.</p>

<p>We have mainly encountered this issue because we have one central function which sets the themes for our many different types of charts.
However, on adding a new heatmap option, I have encountered this issue.</p>