Brief summary of issue / Description of requested feature:

Text in mudlet's triggers are difficult or impossible to read when using a dark QT5 theme

Steps to reproduce the issue / Reasons for adding feature:

1. Use the qt5ct tool to set the color scheme to "darker"

2. Start mudlet as: QT_QPA_PLATFORMTHEME=qt5ct mudlet
3. Take a look at some triggers

Error output / Expected result of feature

1. The name of the trigger is invisible, because it's white on white.

2. The titles of dialog boxes are nearly invisible because they use white text on bright backgrounds.

3. Substring match text is difficult to see because it's black text on a dark gray background.

4. Perl regex match text is difficult to see because it's dark blue text on a dark gray background.

Below is a screenshot of what this looks like on my system. Note that the selected trigger does actually have a name, but it can't be seen because it's white text on a white background:

Extra information, such as Mudlet version, operating system and ideas for how to solve / implement:

Mudlet 3.15.0, Gentoo Linux amd64

I suspect that this issue is due to Mudlet assuming that the user is using a light theme, where the chosen colors are readable. It would be nice if Mudlet either:

1 - Detected the theme and adjusted its colors to be readable on the theme, whether the theme was light or dark.

2 - Used colors that are readable on all themes (or at least on both light and dark themes).

3 - Allowed the user to adjust all the different colors used in the GUI for themselves, so they could fix this issue manually if need be.

4 - Be more compliant with the chosen theme, so that the user never sees bright backgrounds or dark forgrounds when they've selected a dark theme.