feat: disable copy css button

[iamstratos]

Type of Change

• [ ] Bugfix (a fix that does not break existing functionality)
• [x] Enhancement (new feature/minor improvement)
• [ ] Breaking change (fix or feature that would cause existing functionality to break)

What is Changed

• Added disabled to Copy CSS button when there are no added gradients.
• Added global styles for disabled buttons

Comments

Checklist

• [x] I have read the CONTRIBUTING guideline.
• [x] I have given this pull request a clear and descriptive title
• [x] I have clearly described the changes that this pull request makes
• [x] I have included relevant information or comments