Adding environment variable configuration and UI beautification

Description

This PR adds environment variable configuration and UI beautification to the project. It includes the following changes:

Environment Variable Configuration

Added new environment variables to the sweep.yaml file.
Updated the docusaurus.config.js file to use the new environment variables.

UI Beautification

Updated the src/css/custom.css file with new styles for UI beautification.
Updated the src/components/HomepageFeatures/index.js file to use the new styles.
Updated the src/pages/index.js file to use the new styles.

Summary

This PR adds environment variable configuration and UI beautification to enhance the project. It ensures that the project is properly configured with the necessary environment variables and improves the visual appeal of the UI components. These changes have been thoroughly tested and are ready for review and merge.

Fixes #4.

To checkout this PR branch, run the following command in your terminal:

git checkout sweep/add-env-var-ui-beautification

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chunbaiseakuang / docusaurus-2