css Update introjs-nassim.css

[i-m-sonu]

Checklist

• I have followed the Contributor Guidelines.
• The code has been thoroughly tested in my local development environment with flake8 and pylint.
• The code is Python 3 compatible.
• The code follows the PEP8 styling guidelines with 4 spaces indentation.
• This Pull Request relates to only one issue or only one feature
• I have referenced the corresponding issue number in my commit message
• I have added the relevant documentation.
• My branch is up-to-date with the Upstream master branch.

Changes proposed in this pull request

Your development environment

• OS: x
• OS Version: x
• Python Version: x