dots/usr/share/themes/Dracula/gtk-3.20/widgets/_frames.scss

/**********
 * Frames *
 **********/
frame > border,
.frame {
  box-shadow: none;
  margin: 0;
  padding: 0;
  border-radius: 0;
  border: 1px solid $borders_color;

  &.flat { border-style: none; }

  &:backdrop { border-color: $backdrop_borders_color; }
}

actionbar > revealer >  box {
  padding: 6px;
  border-top: 1px solid $borders_color;

  &:backdrop { border-color: $backdrop_borders_color; }
}

scrolledwindow {
  viewport.frame { // avoid double borders when viewport inside scrolled window
    border-style: none;
  }

  // This is used when content is touch-dragged past boundaries.
  // draws a box on top of the content, the size changes programmatically.
  overshoot {
    &.top {
      @include overshoot(top);

      &:backdrop { @include overshoot(top, backdrop); }
    }

    &.bottom {
      @include overshoot(bottom);

      &:backdrop { @include overshoot(bottom, backdrop); }
    }

    &.left {
      @include overshoot(left);

      &:backdrop { @include overshoot(left, backdrop); }
    }

    &.right {
      @include overshoot(right);

      &:backdrop { @include overshoot(right, backdrop); }
    }
  }

  // Overflow indication, works similarly to the overshoot, the size if fixed tho.
  undershoot {
    &.top { @include undershoot(top); }

    &.bottom { @include undershoot(bottom); }

    &.left { @include undershoot(left); }

    &.right { @include undershoot(right); }
  }

  junction { // the small square between two scrollbars
    border-color: transparent;
    // the border image is used to add the missing dot between the borders, details, details, details...
    border-image: linear-gradient(to bottom, $borders_color 1px, transparent 1px) 0 0 0 1 / 0 1px stretch;
    background-color: $scrollbar_bg_color;

    &:dir(rtl) { border-image-slice: 0 1 0 0; }

    &:backdrop {
      border-image-source: linear-gradient(to bottom, $backdrop_borders_color 1px, transparent 1px);
      background-color: $backdrop_scrollbar_bg_color;
      transition: $backdrop_transition;
    }
  }
}

//vbox and hbox separators
separator {
  background: transparentize(black, 0.9);
}