Preparation - make the directives caret discoverable

As a user, I want to easily find the directives drop down. 

Currently, the caret doesn't look clickable. We want to change it by applying a visual treatment.

Specs:

• Button size 15px by 15px

• Normal state

  • drop shadow

  • outline stroke grey-02: #666666

  • button color: white

  • caret: grey-02: #666666

• Hover

  • no drop shadow

  • outline stroke blue-02: #0076dc

  • button color blue-02: #0076dc

  • caret:  white

• Selected

  • no drop shadow

  • outline stroke grey-03: #999999

  • button color grey-03: #999999

  • caret: white

Acceptance Criteria

On hover, a tool tip is displayed: "Column transformation"