assets/styles.css

/* Sidebar: left scrollbar*/
#controls_sidebar { direction: rtl; }
#controls_sidebar .gr-accordion,
#controls_sidebar .gr-markdown,
#controls_sidebar .gr-form,
#controls_sidebar .gr-box,
#controls_sidebar .gr-panel,
#controls_sidebar .gr-group,
#controls_sidebar .gr-row,
#controls_sidebar .gr-column,
#controls_sidebar .gr-block,
#controls_sidebar .gr-input,
#controls_sidebar .gr-button,
#controls_sidebar .gr-code,
#controls_sidebar .gr-html,
#controls_sidebar .gr-checkbox,
#controls_sidebar .gr-slider,
#controls_sidebar .gr-dropdown,
#controls_sidebar .gr-radio,
#controls_sidebar .gr-number,
#controls_sidebar .gr-textbox { direction: ltr; }

/* non-visible scrollbar using Webkit */
#controls_sidebar ::-webkit-scrollbar { width: 10px; }
#controls_sidebar ::-webkit-scrollbar-track { background: transparent; }
#controls_sidebar ::-webkit-scrollbar-thumb {
  background: rgba(100, 116, 139, 0.35);
  border-radius: 999px;
  border: 3px solid transparent;
  background-clip: content-box;
}
#controls_sidebar ::-webkit-scrollbar-thumb:hover {
  background: rgba(100, 116, 139, 0.55);
  border: 3px solid transparent;
  background-clip: content-box;
}

/* Firefox adapt */
#controls_sidebar { scrollbar-width: thin; scrollbar-color: rgba(100,116,139,.45) transparent; }