How can I make a pie chart fill 100% of the divit is contained in? The div has a width of 198px and it’s height is 152px.
Additionally I would like to have a linear-gradient effect inside each pie slice, can you advise on how to do that?

You can achieve the full height of the pie chart by setting the
sizeattribute in theplotOptionsof pie and removingmargins,spacingandtitlesfrom the chart.Code
Example (updated the fiddle to point to version 2.2.4)
Here is an example demonstrating this.
As to the linear gradients, I don’t know if they have been implemented yet, but here is an example showing radial gradients.Radial gradients are also part of Highcharts 3.0 now, here is an example
Update
Looks like as of Highcharts 3.0, this is not possible anymore due to the chart auto-scaling within the plot area, an excerpt from their documentation:in my opinion this should not be the case since
dataLabelsare disabled. should probably be logged as a bugUpdate (Aug 2014)
As per Torstein’s comment, this is indeed still possible.
slicedOffsetneeds to be set to0in addition to the margins begin set. (example)