fix repetition of tool images

### Steps to reproduce
1. visit any of the tools on [carvel.dev](https://carvel.dev/ytt/)
2. See the image tiles oddly on wide screens

### Expected
Image is fixed, doesn't overlap with text and doesn't repeat

### Actual
image overlaps text and repeats

### Notes
- the carvel.dev page does this correctly using `background-size: cover`

Start by inspecting the tool pages on carvel.dev and the image-tile styling, using the reported wide-screen overlap and repetition as the reproduction case. Compare the relevant background behavior with the note about background-size: cover; done means the image is fixed, does not overlap text, and does not repeat on wide screens.

Written by the indexing model from the issue text.