[ADD] Email Validation + UI Corrected + Typo fix

[nikhil-amin]

Description

• Added email validation to the input. Input will now be first validated and username/domain shall be displayed only for valid email IDs. "Invalid Email" message will be displayed otherwise.
• Typo of input "Remander" corrected to "Remainder"
• UI of smart calculater fixed

Fixes #(issue_no)

• Issue_no: <insert your issue no here>
• Not applicable

Type of change

Choosing one or more options from the following as per the nature of your Pull request.

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

Checklist:

Please tick all the boxes that are fulfilled by your Pull Request.

• I have named my files and folder, according to this project's guidelines.
• My code follows the style guidelines of this project.
• I have commented on my code, particularly in hard-to-understand areas.
• I have created a helpful and easy to understand README.md, according to the given README_TEMPLATE.
• My changes do not produce any warnings.

[nikhil-amin]

Hey, thanks for the merge. Can you please add hacktoberfest-accepted label on this PR?