Hardcoded breakpoint in AppRouter

[bgoyarts]

Describe the bug
It is possible inside a custom theme styles/configs/style.json to specify breakpoints for your theme. However, inside my-account a hardcoded breakpoint is used

my-account/react/components/AppRouter.tsx

Line 75 in 670b0b8

<Media query="(max-width: 45em)">

. This conflicts with the generated tachyons file from the supplied config. Result of this is that certain elements disappear in a empty space between breakpoints. An example would be the back button inside the pageHeader.

To Reproduce

1. Use the following breakpoints for your app styles/config/style.json

    {
      "s": 20
    },
    {
      "ns": {
        "value": 40,
        "minWidth": true
      }
    },
    {
      "m": {
        "value": 40,
        "minWidth": true
      }
    },
    {
      "l": {
        "value": 64,
        "minWidth": true
      }
    },
    {
      "xl": {
        "value": 80,
        "minWidth": true
      }
    }
  ],

2. Set your screen to a width of 650px
3. Open the profile page
4. See that the back button is not rendered

Expected behavior
Back button should be visible

Screenshots