Title of the Pull Request

fix: "Buy our E-book" button visibility in night mode

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Related Issue

Closes: #866

Description

The "Buy our E-book" button was not visible in night mode due to insufficient contrast with the background. Updated the button's CSS in assets\css\darkmode.css to ensure it has a suitable color in night mode for better visibility. Added a contrasting background color and text color to the button to maintain readability across themes.

After made Change how it look:

Type of change

What sort of changes have you made:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, local variables)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the code style of this project.
• I have followed the contribution guidelines
• I have performed a self-review of my own code.
• I have ensured my changes don't generate any new warnings or errors.
• I have updated the documentation (if necessary).
• I have resolved all merge conflicts.