I'm using Skeleton (http://getskeleton.com/) for simple css - on desktop it's ok, but on an iPhone the text in button is cropped - see picture.
Here is my simple HTML code:
<html>
<head>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/skeleton/2.0.4/skeleton.min.css">
</head>
<body>
<form id="myform">
jojo
<input class="u-full-width" type="text" dir="ltr" id="user_input" />
<input class="button-primary" value="Go!" type="submit">
</form>
</body>
</html>
Fiddle here: https://jsfiddle.net/tdycs7ar/1/
I'm guessing this has to do with the line-height on your element, pushing the content down on scaling. This could be tested with a simulator on xcode if you have access to a mac.
The easy solution would be to remove the line-height attribute from the button? It doesn't seem to be required for the styling to work.