Answers for "button border-radius:"

border radius circle button

.btn {
  height: 300px;
  width: 300px;
  border-radius: 50%;
  border: 1px solid red;
}

rounded corners css button

.btn{
    border: none;
    padding: 7px 26px;
    text-align: center;
    color: white;
    background: #dc3545;
    border-radius: 40px;
}