[KWoC] Refactor: BMI Calculator

[supr1yo]

Describe your changes (Mandatory)

• Removed arrows from number input field
• Changed styling property for input fields
• Tweaked placeholders a bit.

Issue ticket number and link (Mandatory)

Screenshots of your project, whatever you have added. (Mandatory)

Checklist before requesting a review

• I have performed a self-review of my code
• If it is a new project, I have done thorough tests.
• Have you updated the README file of the repository and added the name of the project in it?
• Have you added a README.md file inside the directory of your project and explained it there properly (with images)?
• Have you updated the script.js file so that the project is visible in the website?

[shrey141102]

good work