Change fonts and colors palette

[EugenioPetulla]

Description

Change fonts and colors palette.

• Change font family (Rubik)
• Change color palette to more consistent one: #14CC9E, #0E8F7E, #C6FFF7

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings