refactor: Removes the CSS files from the Treemap plugin

[michael-s-molina]

SUMMARY

This PR removes the CSS files from the Treemap plugin using Emotion. It also adjusts the styles to match theme configuration and existing components.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

Check that the plugin is very similar to the previous version. We may have color, font, and opacity differences due to theme adjustments.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #19486 (d079a18) into master (11bf0d0) will increase coverage by 0.00%.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master   #19486   +/-   ##
=======================================
  Coverage   66.59%   66.59%           
=======================================
  Files        1676     1677    +1     
  Lines       64191    64215   +24     
  Branches     6525     6537   +12     
=======================================
+ Hits        42746    42762   +16     
- Misses      19746    19754    +8     
  Partials     1699     1699           

Flag	Coverage Δ
javascript	51.32% <0.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...s/legacy-plugin-chart-treemap/src/ReactTreemap.jsx	0.00% <0.00%> (ø)
...plugins/legacy-plugin-chart-treemap/src/Treemap.js	0.00% <ø> (ø)
...d/components/DashboardBuilder/DashboardBuilder.tsx	70.88% <0.00%> (-1.85%)	⬇️
...rontend/src/dashboard/components/DashboardGrid.jsx	62.50% <0.00%> (-0.55%)	⬇️
...rontend/src/dashboard/containers/DashboardGrid.jsx	100.00% <0.00%> (ø)
...nd/src/dashboard/components/gridComponents/Tab.jsx	83.67% <0.00%> (+3.18%)	⬆️
...erset-frontend/src/components/EmptyState/index.tsx	74.35% <0.00%> (+5.12%)	⬆️

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