Added Light/Dark Theme

[KooXinTong]

Fixes #22

Added dark light theme but using toffle button

• Added css to get dark and light theme
• modify the html style and add style sheet

Deploy your changes to github page or netlify and mention deployment link:

Add the deployment link here.

Describe if there is any unusual behaviour of your code(Write NA if there isn't)

N.A.

Additional context (OPTIONAL)

the button

dark theme

light theme

Test plan (OPTIONAL)

Toogle the light/dark button, the background of home page should become white or black.

Checklist

• I have mentioned related issue number in PR description.
• I have added screenshots and related demo links of my changes..
• The title of my pull request is a short description of the requested changes.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• [] I have updated the documentation accordingly.
• [] Open Source Program names(OPTIONAL: If you participated in any open-source program then please mention the program name here)

[QAZIMAAZARSHAD]

Looks nice.

Why did you close the PR?