dots/usr/share/themes/Dracula/gtk-4.0/widgets/_sidebar.scss

/***********
 * Sidebar *
 ***********/
.sidebar,.nautilus-window .navigation-sidebar {
  border-style: none;
  border-width: 0;
  background-color: mix($bg_color, $base_color, 50%);
  .frame{
    border: none;
  }

  @at-root %sidebar_left,
  &:dir(ltr),
  &.left,
  &.left:dir(rtl) {
    border-right: none;
    border-left-style: none;
  }

  @at-root %sidebar_right
  &:dir(rtl),
  &.right {
    border-left: 1px solid $borders_color;
    border-right-style: none;
  }

  &:backdrop {
    background-color: $backdrop_sidebar_bg_color;
    border-color: $backdrop_borders_color;
    transition: $backdrop_transition;
  }

  list { background-color: lighten($bg_color, 0.77%); }
  row{
    padding: 2px 12px;
    &:selected{
      &:backdrop{
        background: transparentize($backdrop_selected_bg_color, 0.3);
        label{
          color: $backdrop_selected_bg_color;
        }  
      }
      &:hover{
        background-color: transparentize($selected_bg_color, 0.2);
      }
      background: transparentize($selected_bg_color, 0.4);
      color: $purple;
      label{
        color: $purple;
      }
    }
  }

    //elementary os file manager
    &.source-list{
      background-color: $headerbar_color; 
      color: #F2EFEA; 
      padding: 4px 0px;
      &.view{
  
      &:selected {
        &:active { box-shadow: inset 0 2px 3px -1px transparentize(black, 0.5); }
  
        &.has-open-popup,
        &:hover { background-color: transparentize($selected_bg_color, 0.2); }
  
        &:backdrop { background-color: $backdrop_selected_bg_color; }
      }
        &:hover, iconview.source-list:hover { 
            background-color: if(variant == light, transparentize($base_color, 0.4), transparentize($base_color, 0.4)); 
        }
      }
    }

  paned & { &.left, &.right, &.left:dir(rtl), &:dir(rtl), &:dir(ltr), & {
    border-style: none;
    border-color: $borders_color;
  }
}
}

stacksidebar {
  &.sidebar {
    &:dir(ltr),
    &.left,
    &.left:dir(rtl) { list { @extend %sidebar_left; }}

    &:dir(rtl),
    &.right { list { @extend %sidebar_right; }}
  }

  row {
    padding: 10px 4px;

    > label {
      padding-left: 6px;
      padding-right: 6px;
    }

    &.needs-attention > label {
      @extend %needs_attention;

      background-size: 6px 6px, 0 0;
    }
  }
}

placessidebar {
  > viewport.frame { border-style: none; }

  row {
    &.sidebar-new-bookmark-row { color: $selected_bg_color; }

    &:drop(active):not(:disabled) {
      &, label, image { color: $drop_target_color; }

      box-shadow: inset 0 1px $drop_target_color,
                  inset 0 -1px $drop_target_color;

      &:selected {
        &, label, image { color: $selected_fg_color; }
        background-color: $drop_target_color;
      }
    }
  }
}