one-dark/gtk-3.0/sass/ui/sidebar.scss

//
// Sidebar
//
.sidebar {
  border-style: none;
  background-color: lighten($bg_color, 2%);

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

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

  list {
    background-color: $base_color;
  }

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

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

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

  row {
    padding: 10px 4px;

    > label {
      padding-left: 6px;
      padding-right: 6px;
    }
    &.needs-attention {
      background-image: radial-gradient(
        circle closest-side at 5% 25%,
        $destructive_color 0%,
        $destructive_color 100%,
        transparent 100%
      );
      background-size: 70px;
      background-position: 4px;
      background-repeat: no-repeat;
    }
    &.activatable:selected.needs-attention {
      background-image: radial-gradient(
        circle closest-side at 5% 25%,
        $selected_fg_color 0%,
        $selected_fg_color 100%,
        transparent 100%
      );
      background-size: 70px;
      background-position: 4px;
      background-repeat: no-repeat;
    }
  }
}

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

  row {
    // Needs overriding of the GtkListBoxRow padding
    min-height: 30px;
    padding: 0px;
    // Using margins/padding directly in the SidebarRow
    // will make the animation of the new bookmark row jump
    > revealer {
      padding: 0 10px;
    }
    image.sidebar-icon {
      &:dir(ltr) {
        padding-right: 8px;
      }
      &:dir(rtl) {
        padding-left: 8px;
      }
    }
    label.sidebar-label {
      &:dir(ltr) {
        padding-right: 2px;
      }
      &:dir(rtl) {
        padding-left: 2px;
      }
    }
    @at-root button.sidebar-button {
      min-width: 22px;
      min-height: 22px;
      margin-top: 2px;
      margin-bottom: 2px;
      padding: 0;
      @extend %button_basic_flat;
      border-radius: 100%;
      -gtk-outline-radius: 100%;

      &:not(:hover):not(:active) > image {
        opacity: 0.5;
      }
    }

    &.sidebar-placeholder-row {
      padding: 0 8px;
      min-height: 2px;
      background-image: _solid($drop_target_color);
      background-clip: content-box;
    }

    &.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;
      }
    }
  }
}







//
// PlacesView
//
placesview {
  .server-list-button > image {
    transition: 200ms $ease-out-quad;
    -gtk-icon-transform: rotate(0turn);
  }

  .server-list-button:checked > image {
    transition: 200ms $ease-out-quad;
    -gtk-icon-transform: rotate(-0.5turn);
  }

  // this selects the "connect to server" label
  > actionbar > revealer > box > label {
    padding-left: 8px;
    padding-right: 8px;
  }
}







//
// Paned
//
paned {
  > separator {
    min-width: 1px;
    min-height: 1px;
    -gtk-icon-source: none;
    border-style: none;
    background-color: transparent;
    background-image: _solid($borders_color);
    background-size: 1px 1px;

    &:selected {
      background-image: _solid($selected_bg_color);
    }

    &.wide {
      min-width: 5px;
      min-height: 5px;
      background-color: transparent;
    }
  }

  &.horizontal > separator {
    background-repeat: repeat-y;
    margin: 0 -3px 0 -3px;
    padding: 0 3px 0 3px;
    background-position: center;

    &.wide {
      margin: 0;
      padding: 0;
      background-repeat: no-repeat;
      background-position: center;
      background-image: -gtk-scaled(
        url('assets/pane-separator-vertical.png'),
        url('assets/pane-separator-vertical@2.png')
      );
      background-size: 2px 24px;
    }
  }

  &.vertical > separator {
    margin: -3px 0 -3px 0;
    padding: 3px 0 3px 0;
    background-repeat: repeat-x;
    background-position: center;

    &.wide {
      margin: 0;
      padding: 0;
      background-repeat: no-repeat;
      background-position: center;
      background-image: -gtk-scaled(
        url('assets/pane-separator.png'),
        url('assets/pane-separator@2.png')
      );
      background-size: 24px 2px;
    }
  }
}