Fix mobile presentation for "Evolve your API without versions"

[francisfuzz]

Hi there @leebyron 👋

I'm pinging you because the changes proposed here modify a line in site/_css/index.less, which was last worked on in 79e3bb1 as a part of the work done in #76.

If you're not maintaining this part of the code anymore, please let me know if there's a better person I should get in touch with about this change. Thanks! 🙇

Context

Let's say I navigate to http://graphql.org, where my window has width of less than 1020px.

Here's how the Evolve your API without versions section looks like when viewed from a window whose width is less than 1020px:

This pull request modifies site/_css/index.less to use the padding-right attribute instead of the right attribute so it doesn't look like that anymore:

[leebyron]

Thanks for your investigation into this! This change seems like patching a symptom rather than fixing the root issue though. Typically percentage based paddings can cause skew in the actual pixel where elements end up.

[leebyron]

The root issue seemed to be an over-application of text-align: center which makes sense since the broken screenshot shows the + centered in the line.