Changes to Bar Graph Report Color Using CSS Are Not Sticking

Hi there!
I'm using the CSS code below to change the colors of a bar graph on a report. When viewing in the app, the changes only appear when I initially log in or if I refresh the page.
If I navigate to another page in the app, and then back to the page with the report, the bar graph once again displays in the default light blue color.
The only time I can see the changes to the colors is if I navigate to the page with the report and manually refresh the browser, or when I initially log in.
Any idea what's going on?
I've cleared the browser cache, cookies, etc., and tried incognito mode and even another computer that has never been used to access the app.
Thank you in advance!
#kn-report-view_8-1 #highcharts-0 > svg > g > g > rect:nth-child(1) {

#kn-report-view_8-1 #highcharts-0 > svg > g > g > rect:nth-child(2) {

#kn-report-view_8-1 #highcharts-0 > svg > g > g > rect:nth-child(3) {