Several Updates

[Golodhros]

In this commit, I tackled:

• Fixing color selector 'undefined' element at the end
• Updating Stacked Area Chart demo code example by simplifying the text and removing comments
• Fixed brush styling
• Adjusted x time axis by reducing the time range necessary to show the years and months

Motivation and Context

Updates on docs and X-axis, fixes brush styling

How Has This Been Tested?

Ran tests and checked visually

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.