Added Light/Dark Theme

[KooXinTong]

Fixes #22

Describe the changes you've made

• edit home page style
• Added css for the feature.

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

NA

Additional context (OPTIONAL)

Added toggle button

Test plan (OPTIONAL)

• Action: Toogle the button
• Expected: The background in home page should change to white or black depands on the toggle button

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)