How to make a button round?

Question

css

How to make this button the same as this one in the photo? Oval, in the sense

Here is the code for the "wrong button":

/* Кнопка закрыть */
.close {
    color: white;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: #000;
    text-decoration: none;
    cursor: pointer;
}

Here is the whole code, just in case

<style>
/* Стиль модального окна Mobirise */
.popup {
    display: none; /* Hidden by default */
    position: fixed; /* Stay in place */
    z-index: 1; /* Sit on top */
    padding-top: 100px; /* Location of the box */
    left: 0;
    top: 0;
    width: 100%; /* Full width */
    height: 100%; /* Full height */
    overflow: auto; /* Enable scroll if needed */
    background-color: rgb(0,0,0); /* Fallback color */
    background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}

/* Контент модального окна Mobirise */
.popup-content {
    position: relative;
    background-color: #fefefe;
    margin: auto;
    padding: 0;
    border: 1px solid #888;
    width: 80%;
    box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19);
    -webkit-animation-name: animatetop;
    -webkit-animation-duration: 0.4s;
    animation-name: animatetop;
    animation-duration: 0.4s
}

/* Включаем анимацию */
@-webkit-keyframes animatetop {
    from {top:-300px; opacity:0} 
    to {top:0; opacity:1}
}

@keyframes animatetop {
    from {top:-300px; opacity:0}
    to {top:0; opacity:1}
}

/* Кнопка закрыть */
.close {
    color: white;
    float: right;
    font-size: 28px;
    font-weight: bold;
}

.close:hover,
.close:focus {
    color: #000;
    text-decoration: none;
    cursor: pointer;
}

.popup-header {
    padding: 2px 16px;
    background-color: #5cb85c;
    color: white;
}

.popup-body {padding: 2px 16px;}

.popup-footer {
    padding: 2px 16px;
    background-color: #5cb85c;
    color: white;
}
</style>

<!-- Код попап окна Mobirise-->
<div id="mypopup" class="popup">
  <!-- Контент попап окна Mobirise -->
  <div class="popup-content">
    <div class="popup-header">
      <span class="close">&times;</span>
      <h2>popup Header</h2>
    </div>
    <div class="popup-body">
      <p>Some text in the popup Body</p>
      <p>Some other text...</p>
    </div>
    <div class="popup-footer">
      <h3>popup Footer</h3>
    </div>
  </div>
</div>

Answer 1

jsfiddle.net/qnGKj/3392

Answer 2

htmlbook.ru/css/border-radius is this?

Answer 3

border-radius: 50px
https://codepen.io/anon/pen/PQgGgo