QSlider different color for add-page (width should be constant)

Question

I am currently developing a GUI using Qt6. I want to create a custom vertical slider using stylesheets. I want the bottom part of the slider, right below the handle, have a different color, but when I try to manipulate the "add-page" section of the slider's stylesheet, the width is not constant anymore and it looks like this:

I expect the width of the groove area of the slider to stay the same, on top and below the handle. Here's my code so far:

QSlider:vertical
{
  min-height: 100px;
  min-width: 20px;
  background: none;
}
QSlider::groove:vertical
{
  background: rgb(43, 43, 43); 
  border: 1px solid rgb(43, 43, 43); 
  border-radius: 2px;
  width: 4px;
  margin: 0px 17px;
}
QSlider::handle:vertical
{
  background: white;
  border: 1px solid white;
  border-radius: 3px;
  top: 14px;
  bottom: 14px;
  margin: -15px -7px;
  min-width: 30px;
  min-height: 30px;
}
QSlider::add-page:vertical
{
  background: white;
}

When I remove the add-page section from the stylesheet, the slider looks like this:

As you can see, the bottom part is not white anymore, but the width does look nice now.

Answer 1

Move the definition of your margin so it affects the groove and the add-page together (and the sub-page if you want). The gist of it, where I put the bottom part red to make the difference with the handle visible, is:

QSlider::groove:vertical,
QSlider::add-page:vertical
{
  margin:0px 17px;
}
QSlider::add-page:vertical
{
  background-color: red;
}

And the complete stylesheet based on the one in your question:

QSlider:vertical
{
  min-height: 100px;
  min-width: 20px;
  background: none;
}
QSlider::groove:vertical
{
  background: rgb(43, 43, 43); 
  border: 1px solid rgb(43, 43, 43); 
  border-radius: 2px;
  width: 4px;
}
QSlider::handle:vertical
{
  background: white;
  border: 1px solid white;
  border-radius: 3px;
  top: 14px;
  bottom: 14px;
  margin: -15px -7px;
  min-width: 30px;
  min-height: 30px;
}
QSlider::groove:vertical,
QSlider::add-page:vertical
{
  margin:0px 17px;
}
QSlider::add-page:vertical
{
  background-color: red;
}