sidebar scaling

hey, i have a problem i have this sidebar https://bcdadvies.nl/ and it has to go to the end of the page but it needs to scale with the text, now it doesn’t i can’t put only 100% height on it as it don’t show the color of the sidebar to the very end of the page. would be very grateful for help.
if there is a plugin for this kind of sidebars, that would also help, but of course it’s better to edit in code.