Where has .btn-default gone in Bootstrap 4?

Question

According to the Bootstrap 3 to Bootstrap 4 migration docs:

Buttons

• Renamed .btn-default to .btn-secondary.

But

Answer 1

add this css to your stylesheet file problem gone

.btn-default {
    color: #333;
    background-color: #fff;
    border-color: #ccc;
}
.btn-default:focus {
    color: #333;
    background-color: #e6e6e6;
    border-color: #8c8c8c;
}
.btn-default:hover {
    color: #333;
    background-color: #e6e6e6;
    border-color: #adadad;
}
.btn-default:active {
    color: #333;
    background-color: #e6e6e6;
    border-color: #adadad;
}