it's not possible to use css to override the colours of SVG URLs that are used as background images because those SVGs are not actually in DOM and can't be targeted by CSS. We've had previous issues that needed to be fixed:

• fix: Embed play/pause indicator should render correctly in high contrast mode #27213
• fix: SplitButton should display correctly in high contrast mode #27137

We should go through all the SVG URLs in northstar and do the same treatment as the PRs above: overriding URL colour in the forced colours theme.

• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/pointerSvgUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Toolbar/activeIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Alert/dismissIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Carousel/paddleIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Checkbox/checkboxIndeterminateIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Checkbox/checkboxIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Dropdown/checkableIndicatorUrl.ts
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Embed/pauseIndicatorUrl.ts fix: Embed play/pause indicator should render correctly in high contrast mode #27213
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Embed/playIndicatorUrl.ts fix: Embed play/pause indicator should render correctly in high contrast mode #27213
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/SplitButton/toggleIndicatorUrl.ts fix: SplitButton should display correctly in high contrast mode #27137
• https://github.com/microsoft/fluentui/blob/master/packages/fluentui/react-northstar/src/themes/teams/components/Tree/checkboxIndicatorIndeterminatedUrl.ts