fix: charts tooltip theme color for darkmode

[Amirthananth]

Description

The chart tooltip text visibility is affected in dark mode. Introduced a different bg and fg color for the charts to make the text suit for both themes (light and dark).

What type of PR is this? (check all applicable)

• [ ] 💡 Feature
• [x] 🐛 Bug Fix
• [ ] 📝 Documentation Update
• [x] 🎨 Style
• [ ] 🧑‍💻 Code Refactor
• [ ] 🔥 Performance Improvements
• [ ] ✅ Test
• [ ] 🤖 Build
• [ ] 🔁 CI
• [ ] 📦 Chore (Release)
• [ ] ⏩ Revert

Related Tickets & Documents

This PR fixes #12

Mobile & Desktop Screenshots/Recordings

Light Mode

Dark Mode

Steps to QA

1. Change theme to light/dark mode
2. Hover on top of the graph and try to read the data

Added to documentation?

• [ ] 📜 README.md
• [x] 🙅 no documentation needed

[optional] Are there any post-deployment tasks we need to perform?

[optional] What gif best describes this PR or how it makes you feel?

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[Amirthananth]

@Codehagen Do review and let me know. I've also added a few styles to the funnel chart to keep it consistent with the other chart.