Debian Mate Desktop Eclipse scoll bar slider button size huge

I am on **Debian** Buster, **Mate Desktop** theme Menta, OpenJdk 11.0.9.1, **eclipse 2020-06**. My scroll bar sliders in eclipse are huge. I tried resizing them by a custom gtk-3 css file but this did only change the bar itself but not the buttons. *gedit* does apply the css settings. See bewlo: It does not matter if **theming in eclipse** is on or off (I restarted) or the used eclipse theme. I read about the setting and tried changing -Dswt.enable.themedScrollBar=false / true in eclipse.ini, didn't change a thing. **gtk-3 css** The ~/.config/gtk-3.0/gtk.css I tried. Pretty much the default values from GTKTheme

css
    scrollbar slider {
      /* Size of the slider */
      min-width: 6px;
      min-height: 6px;
      border-radius: 6px;
      -GtkRange-slider-width: 6;
      -GtkRange-stepper-size: 6;
      -GtkRange-stepper-spacing: 0;
      -GtkRange-trough-border: 1;
      -GtkRange-arrow-displacement-x: 0;
      -GtkRange-arrow-displacement-y: 0;
      -GtkRange-activate-slider: FALSE;
      -GtkRange-trough-side-detrails: FALSE;
    }

**gtk-2 gtkrc** I tried setting ~/.config/gtk-2.0/gtkrc

css
    style "scroll"
    {
     GtkScrollbar::slider-width = 6
    }
    class "*" style "scroll"

**Side note:** It looks even worse using the dark eclipse theme as the slider colour does not change.