The sample page:
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Button test</title>
<style>
* { border: none; margin: 0; padding: 0; }
body { padding: 5em; }
span { background: lightblue; display: inline-block; }
button { background: red; outline: 1px solid red }
button div { background: yellow; }
button::-moz-focus-inner {
padding: 0;
border: 0;
}
button {
-webkit-appearance: none;
-webkit-box-sizing: content-box;
-webkit-box-align: start;
-webkit-border-fit: lines;
-webkit-margin-collapse: discard;
}
</style>
</head>
<body>
<span>Adjacent text</span><button><div>Button</div></button>
</body>
</html>
Here is the image:

You can see the extra white padding in the button. Is it possible to get rid of that padding in Safari browser?
The problem is fixed in some version of Safari, I’m not sure what exactly, but in latest (5.1.5) it works for me.