Update the style of modals/pop-up windows.

[jianyuan-zhan]

Description

Please provide a summary of the pull request and the issue it fixes. Please add necessary details, context, dependencies, explanation of when review is needed (see next section), etc.

Fixes #1054

Review Time Estimate

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Type of changes

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• [ ] Bug fix (non-breaking change which fixes an issue).
• [x] New feature (non-breaking change which adds functionality).
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected).
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Checklist:

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• [ ] I have signed the Rokwire Contributor License Agreement (CLA). (Any contributor who is not an employee of the University of Illinois whose official duties include contributing to the Rokwire software, or who is not paid by the Rokwire project, needs to sign the CLA before their contribution can be accepted.)
• [x] I have updated the CHANGELOG.
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• [x] I have performed a self-review of my own code.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] My change requires updating the documentation.
• [ ] I have made necessary changes to the documentation.
• [ ] I have added tests related to my changes.
• [ ] My changes generate no new warnings.
• [ ] New and existing unit tests pass locally with my changes.
• [ ] Any dependent changes have been merged and published in downstream modules.

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[sandeep-ps]

The current changes look good to me. Thanks.

@minump, Could you please resolve your comment if you are satisfied with the changes? Thanks. @clav1d or @bingzhang, please resolve the merge conflicts. Thanks.