As may you aware some applications comes in a dark theme version that break with the light elementary OS theme. If you are looking for how to make the dark apps light to match the rest of the themes this is the place.
You can actually set different apps with different themes.
First you need a menu editor for this, type in terminal:
sudo apt-get install com.github.donadigo.appeditor
You will now find the Appeditor in System Tools. Open it.
Find eg. Screencast and in command box of it you will add
So it will say
env GTK_THEME=elementary com.github.artemanufrij.screencast %U
Find the rest of the dark theme apps and do the exact same thing with them.