rounded corners css button

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

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

<Style TargetType="Button" x:Key="RoundButton">
    <Style.Resources>
        <Style TargetType="Border">
            <Setter Property="CornerRadius" Value="5" />
        </Style>
    </Style.Resources>
</Style>