If you want to change the input sizes on that page only add this to Graphene’s custom CSS feature:
#loginform input {
font-size: 24px;
height: 30px;
}
and play around with the sizes. (The sizes are exaggerated in this example so that you can see when they take effect.)
If you want to change the input size everywhere, use this code instead:
input[type="text"], input[type="email"], input[type="password"], input[type="search"], input[type="tel"], input[type="time"], input[type="url"], input[type="date"], input[type="datetime"], input[type="datetime-local"], textarea {
font-size: 24px;
height: 30px;
}