Fix Staking dapp dark mode styles

[vbaranov]

#2647

Motivation

Changelog

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 7f3c39ac193b8d340ef1e03d0e1f76b47490d7bd-PR-3365

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 18 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-1.3%) to 67.558%

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Files with Coverage Reduction	New Missed Lines	%
lib/block_scout_web/channels/address_channel.ex	2	36.96%
lib/block_scout_web/notifier.ex	2	82.95%
lib/block_scout_web/controllers/stakes_controller.ex	14	57.45%

Totals
Change from base Build f66e21691b40d542a4c1f1cadcc2f6e92d53448e:	-1.3%
Covered Lines:	2047
Relevant Lines:	3030

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💛 - Coveralls