Change a magic number to somethign else for a width on sign-up page's CSS

[cychu42]

What would you like to be added:
In PR #3743, there was use of a magic number for a width to handle overflow. One should look at the width of surrounding containers to set that width accordingly.

Why would you like this to be added:
It's a better practice and to fit with the design of the page. I would like to handle this myself.

[AmasiaNalbandian]

For "services" like this, I would suggest we make it reusable to use elsewhere in the project.

[cychu42]

Sorry, can you clarify what you mean by "this"? Do you mean the overflow handling with use of eclipses?