I suggest adding input[type=number]
to the theme field styling:
input[type=text],input[type=email],input[type=url],input[type=password],input[type=tel],input[type=search],textarea {
background:#FAFAFA;
color:#666;
border:1px solid #ccc;
border-radius:0;
padding:10px 15px;
-moz-box-sizing:border-box;
-webkit-box-sizing:border-box;
box-sizing:border-box;
max-width:100%
}
input[type=text]:focus,input[type=email]:focus,input[type=url]:focus,input[type=password]:focus,input[type=tel]:focus,input[type=search]:focus,textarea:focus {
color:#111;
background:#FFF
}
I know I would be able to add some custom CSS to style number fields. But I believe is could be implemented in the theme default css =)