.form-group.span-left, .form-group.span-right {
    width: calc(50% - 10px);
}

.form-group.span-left.half-left, .form-group.span-left.half-right,
.form-group.span-right.half-left, .form-group.span-right.half-right {
    width: calc(25% - 15px);
}

.form-group.span-left.half-left {}
.form-group.span-left.half-right {
    clear: none;
    margin-left: 20px;
}
.form-group.span-right.half-left {}
.form-group.span-right.half-right {
    clear: none;
    margin-right: 20px;
}