You can use the Styling > Advanced menu item to access the Advanced CSS editor. Here you can enter any custom CSS you want to apply to your report. The box below shows you the selectors you will need to use (note also that each widget can have its own custom CSS class, accessed via the widget settings dialog).

.ia-app .ia-report {
/** The report container */
.ia-app .ia-report .ia-report-page {
/** An individual page in the report */
.ia-app .ia-report .ia-report-page .ia-report-widget {
/** An individual widget in the report */

Be careful using the custom CSS editor. The CSS is applied directly to your report without any validation. You should be especially careful about using targeted selectors (i.e. using the class names above and not tag names like “div” or “button”) if you are embedding your report into another website or you can end up applying styles to items outside your report.