Add additional form styles

Form styling isn't perfect yet (though it's a lot better than it used to be).

These styles should make forms look even better (feel free to use standard values, this is just an approximation):

fieldset {
    padding: 1rem;
     border: 1px solid #ced4da;
     margin-top: 1rem;
}
legend {
     padding: 0px 1rem;
     display: inline-block;
     width: auto;
}

label {
     margin-right: .5rem;
     margin-left: .5rem;
}