style: improve light mode layout and background for Expenses and Recent Activity sections

[asr1325]

Description

This PR enhances the light mode styling for the "Expenses by Category" and "Recent Activity" sections.
The changes include:

• Removed extra borders and visual clutter for a cleaner layout.
• Updated background colors of these sections to better match the overall light mode theme and ensure consistent contrast.

Related Issue

Fixes #105

Motivation and Context

The previous light mode layout had mismatched backgrounds and unnecessary borders, which disrupted visual balance and readability.
This update improves UI aesthetics and user experience, especially for users who prefer light mode.

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Enhancement (improvement to an existing feature)
• Breaking change (fix or feature that would cause existing functionality to change)
• Test (adds or updates tests only)
• Documentation (non-code change)

How Has This Been Tested?

• Visually tested both light and dark modes in the dashboard.
• Verified that the "Expenses by Category" and "Recent Activity" sections now have light colored backgrounds in light mode.
• Checked responsiveness and layout consistency across different screen sizes.

Screenshots (if applicable):

Checklist

• My code follows the code style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

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