Fixed buttons color at smart contract section

[YegorSan]

This PR is related to #2652 issue.

@vbaranov As you requested, I've re-created this PR to master branch, and now I am closing #2655 PR with the same update which was added to front-update branch.

Motivation

• Different color of buttons at smart contract page.

Changelog

Bug Fixes

• Fixed color of a "Query" buttons at Read Contract section.

Checklist for your 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 if necessary
• If I added/changed/removed ENV var, I should update the list of env vars in https://github.com/poanetwork/blockscout/blob/master/docs/env-variables.md to reflect changes in the table here https://poanetwork.github.io/blockscout/#/env-variables?id=blockscout-env-variables. I've set master in the Version column.
• If I add new indices into DB, I checked, that they don't redundant with PGHero or other tools

[vbaranov]

@YegorSan please add CHANGELOG entry

[YegorSan]

@vbaranov Hello. Added new CHANGELOG entry.

[vbaranov]

@YegorSan looks like your branch is not rebased onto the master branch of parent repo

[YegorSan]

@vbaranov Hello Victor. Merging conflict was resolved. Could you please review?

[vbaranov]

@YegorSan

Merging conflict was resolved. Could you please review?

Yes, but CHANGELOG entry is missing

[YegorSan]

@vbaranov Changelog is updated.

[vbaranov]

@YegorSan it is not a feature. Let's move to Fix section

[YegorSan]

@vbaranov Moved new entry to fixes.