fix: fix the style of button-dropdown

[Bowen7]

Checklist

• Fix linting errors
• Tests have been added / updated (or snapshots)

Change information

Before:

After:

[codecov]

Codecov Report

Merging #518 (8fbb5f0) into master (95fc6ef) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #518   +/-   ##
=======================================
  Coverage   99.91%   99.91%           
=======================================
  Files         183      183           
  Lines        2453     2453           
  Branches      604      604           
=======================================
  Hits         2451     2451           
  Misses          2        2           

Impacted Files	Coverage Δ
components/button-dropdown/button-dropdown.tsx	100.00% <ø> (ø)

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[unix]

👍 Thanks!