Issue Title: Adding Percentage (%) Feature to the Calculator

Issue Description:

I propose the addition of a percentage (%) feature to the existing calculator web application. This enhancement will provide users with the ability to perform percentage calculations, making the calculator more versatile and user-friendly.

Proposed Changes:

1. Percentage (%) Feature: Implement the percentage feature, allowing users to calculate percentages of numbers easily. The feature should be accessible and intuitive for users.

Rationale:

The addition of the percentage (%) feature is essential for the following reasons:

Enhanced Functionality:

The percentage feature expands the calculator's capabilities, enabling users to calculate percentages, which is a common and valuable calculation in various scenarios.

Improved User Experience:

This addition enhances the user experience, making the calculator more functional and user-friendly.

Additional Information (if available):

If specific guidelines or steps are required for implementing this feature, please provide the necessary information. I am committed to adding the percentage feature effectively and in line with project requirements.

It would be good if we have a screenshot of the UI in the Readme.md

Please, assign me this if the issue is accepted.

Improve overall design using CSS and HTML, make it more appealing.

Add these 4 buttons (must) ...

• Power (^): Calculates a number raised to a specified power. (ex :- 2^3 = 8)
• Modulo (%): Computes the remainder of a division operation. (ex:- 15%4 = 3)
• Square Root (√): Finds the square root of a number. (ex:- √25 = 5)
• Logarithm (log): Calculates the logarithm of a number. (ex:- log 10 = 1)

You can add other buttons, but they should be working. Keep the overall design in mind.

Add new Buttons in this calculator like power, modulo, root, log,... etc.
Keep the overall design in mind.

Create an "Ans" button to use previous answer in calculation.

The display box is exceeding outer div. Fix it using CSS & html.