styling on tabs

## Description

Tab issues: The underlines under the plot and 3D viewer could be a little thicker. They should also align purposefully to the left and right of the tab title/icon.
Also, the color should be white when a tab is active or hovered on (it's currently opposite). Would also be better if words were a little closer to their underlines by a few pixels.

## Expected Behavior

_What did you expect to happen instead?_

## Reproduction

_A minimal example that exhibits the behavior._

## Environment

_Any additional information about your environment. E.g. OS version, python version, browser etc._