Forms: the submitted content doesn't blend in theme

### Impacted plugin

Jetpack

### Quick summary

The submitted content that you'll see after submitting the form styled by the block, therefore it doesn't fit in themes. We should remove the style as much as possible so that it blends in the theme.

This is an example with TT3:

Things to remove:
* Remove the color and font weight from the "go back" link
* Remove the font weight and the margins from he `h4` "Your message has been sent" (why `h4`?)
* Remove the font weight from the field name
* Remove the font weight from the field value
* Remove the width and the paddings from the `.contact-form-submission`

cc: @jeffikus

### Steps to reproduce

1. Add a form
2. Submit the form
3. See the submitted content on the page

### A clear and concise description of what you expected to happen.

_No response_

### What actually happened

_No response_

### Impact

All

### Available workarounds?

No but the platform is still usable

### Platform (Simple and/or Atomic)

_No response_

### Logs or notes

_No response_

Reproduce the Jetpack form submission with the TT3 theme and inspect the submitted-content styles, especially the go-back link, h4 message, field names and values, and .contact-form-submission. The issue names no files or tests; done means those elements inherit the theme without the listed font, margin, width, color, or padding overrides.

Written by the indexing model from the issue text.