CSS-gradients should not only cover the content of an
element but also the padding (but not the border).
<!-- Please describe your changes on the following line: -->
Thanks to @atouchet for catching this.
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix#17387 (github issue number if applicable).
<!-- Either: -->
- [x] These changes do not require tests because gradients are hard to test automatically but you can use [this gist](https://gist.github.com/pyfisch/fa263c8dfc57e5812fe8a4869ad61513) as a manual test.
<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->
<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->
Source-Repo: https://github.com/servo/servo
Source-Revision: 7a80192a820848f5ac04b9f4ffe2e860476579ba