p5.js-web-editor/client/styles/components/_sidebar.scss

.sidebar__file-list {
  border-top: 1px solid $ide-border-color;
}

.sidebar__file-item {
  padding: #{8 / $base-font-size}rem #{20 / $base-font-size}rem;
  color: $light-inactive-text-color;
  cursor: pointer;
  &--selected {
    background-color: $ide-border-color;
  }
}