# Welcome to the Highcharts Gantt JS (gantt) Options Reference

These pages outline the chart configuration options, and the methods and properties of Highcharts objects.

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# tooltip.className

A CSS class name to apply to the tooltip, allowing unique CSS styling for each chart.

Note: The class is applied to the SVG element of the tooltip (the tooltip label group), not to a container div. This allows you to style the tooltip using CSS applicable to SVG elements.

When tooltip.outside is `true`, a separate container div with class `highcharts-tooltip-container` is created as the parent to the SVG tooltip element, but the `className` option is still applied to the SVG element itself, not to the container.