我应该如何将我的非引导模式居中？

Question

我希望将我的非引导模式垂直和水平居中。

我该怎么做？

我已经给出了我用过的 HTML CSS 和 JS 代码。

我现在刚刚输入了随机文本。实际上会有一个注册表单。

这是我所有的模态代码：

<!-- The Modal -->
    <div id="myModal" class="modal center">
      <!-- Modal content -->
      <div class="modal-content">
        <div class="modal-header">
          <span class="close">&times;</span>
          <h2>Modal Header</h2>
        </div>
        <div class="modal-body">
          <p>Some text in the Modal Body</p>
          <p>Some other text...</p>
        </div>
        <div class="modal-footer">
          <h3>Modal Footer</h3>
        </div>
      </div>
    </div>

/* The Modal (background) */
.modal {
  display: none; /* Hidden by default */
  position: fixed; /* Stay in place */
  z-index: 1; /* Sit on top */
  left: 0;
  top: 0;
  width: 100%; /* Full width */
  height: 100%; /* Full height */
  overflow: auto; /* Enable scroll if needed */
  background-color: rgba(255, 255, 255, 0.7); /* Black w/ opacity */
}

/* Modal Content/Box */
.modal-content {
  background-color: #fefefe;
  margin: 15% auto; /* 15% from the top and centered */
  padding: 20px;
  border: 1px solid #888;
  width: 80%; /* Could be more or less, depending on screen size */
}

/* The Close Button */
.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}
/* Modal Header */
.modal-header {
  padding: 2px 16px;
  background-color: #5cb85c;
  color: white;
}

/* Modal Body */
.modal-body {padding: 2px 16px;}

/* Modal Footer */
.modal-footer {
  padding: 2px 16px;
  background-color: #5cb85c;
  color: white;
}

/* Modal Content */
.modal-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);
  animation-name: animatetop;
  animation-duration: 0.4s
}

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

// Get the modal
var modal = document.getElementById("myModal");

// Get the button that opens the modal
var btn = document.getElementById("myBtn");

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// When the user clicks on the button, open the modal
btn.onclick = function() {
  modal.style.display = "block";
}

// When the user clicks on <span> (x), close the modal
span.onclick = function() {
  modal.style.display = "none";
}

Answer 1

由于它是一个fixed 定位元素，您可以使用transform: translate(-50%, -50%); 技巧：

/* The Modal (background) */

#blanket {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  background-color: red;
  /* Black w/ opacity */
}

.modal {
  /* Hidden by default */
  position: fixed;
  /* Stay in place */
  z-index: 1;
  /* Sit on top */
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 100%;
  /* Full width */
  height: 250px;
  /* Full height */
  overflow: auto;
  /* Enable scroll if needed */
}


/* Modal Content/Box */

.modal-content {
  background-color: #fefefe;
  margin: 15% auto;
  /* 15% from the top and centered */
  padding: 20px;
  border: 1px solid #888;
  width: 80%;
  /* Could be more or less, depending on screen size */
}


/* The Close Button */

.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

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


/* Modal Header */

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


/* Modal Body */

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


/* Modal Footer */

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


/* Modal Content */

.modal-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);
  animation-name: animatetop;
  animation-duration: 0.4s
}


/* Add Animation */

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

<div id="blanket">
  <div id="myModal" class="modal center">
    <!-- Modal content -->
    <div class="modal-content">
      <div class="modal-header">
        <span class="close">&times;</span>
        <h2>Modal Header</h2>
      </div>
      <div class="modal-body">
        <p>Some text in the Modal Body</p>
        <p>Some other text...</p>
      </div>
      <div class="modal-footer">
        <h3>Modal Footer</h3>
      </div>
    </div>
  </div>
</div>