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首页 > 解决方案 > 将 HTML 元素的位置更改为绝对位置是否也会更改元素的内容类别？

html - 将 HTML 元素的位置更改为绝对位置是否也会更改元素的内容类别？

问题描述

我正在学习 CSS 的定位和 HTML 的内容类别。而且我想知道为什么在我的浏览器中添加position: absolute;内部header元素会style.css导致一个狭窄的标题元素块。

我希望 header 是一个块级元素并延伸到 body 元素的边框，即触摸我的屏幕边框。

索引.html

<!DOCTYPE html>
<html>
<head>
  <title>Please Participate in Our Survey!</title>
  <link href="https://fonts.googleapis.com/css?family=Oswald:300,700|Varela+Round" rel="stylesheet">
  <link rel="stylesheet" type="text/css" href="style.css">
</head>
<body>

  <header>
    <ul>
      <li>Question 1</li>
      <li>Question 2</li>
      <li>Question 3</li>
      <li>Question 4</li>
      <li>Question 5</li>
      <li>Question 6</li>
    </ul>
  </header>

  <div class="welcome">
    <h1>Welcome to our survey!</h1>
    <p>We're looking forward to getting your answers so we can make sure our products and services are the best they can be!</p>
  </div>

  <div class="question">
    <h4>Question 1</h4>
    <h2>I like participating in physical activity such as running, swimming, or biking.</h2>

    <div class="answer">
      <h3>Disagree</h3>
    </div>

    <div class="answer">
      <h3>Neutral</h3>
    </div>

    <div class="answer">
      <h3>Agree</h3>
    </div>
  </div>

  <div class="question">
    <h4>Question 2</h4>
    <h2>I try to keep up to date with the latest fashion in active wear.</h2>

    <div class="answer">
      <h3>Disagree</h3>
    </div>

    <div class="answer">
      <h3>Neutral</h3>
    </div>

    <div class="answer">
      <h3>Agree</h3>
    </div>
  </div>

  <div class="question">
    <h4>Question 3</h4>
    <h2>I purchase clothing online regularly.</h2>

    <div class="answer">
      <h3>Disagree</h3>
    </div>

    <div class="answer">
      <h3>Neutral</h3>
    </div>

    <div class="answer">
      <h3>Agree</h3>
    </div>
  </div>

  <div class="question">
    <h4>Question 4</h4>
    <h2>I try to buy goods that are designed and/or manufactured in my home country.</h2>

    <div class="answer">
      <h3>Disagree</h3>
    </div>

    <div class="answer">
      <h3>Neutral</h3>
    </div>

    <div class="answer">
      <h3>Agree</h3>
    </div>
  </div>

  <div class="question">
    <h4>Question 5</h4>
    <h2>I look to famous athletes when trying to choose what to wear when training.</h2>

    <div class="answer">
      <h3>Disagree</h3>
    </div>

    <div class="answer">
      <h3>Neutral</h3>
    </div>

    <div class="answer">
      <h3>Agree</h3>
    </div>
  </div>

</body>
</html>

样式.css

body {
  background-color: #FFF;
  margin: 0 auto;
}

header {
  background-color: #466995;
  border-bottom: 1px solid #466995;
  position: absolute; // This line!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  border: thin solid red !important;
}

ul {
  margin: 30px auto;
  padding: 0 20px;
  text-align: center;
}

li {
  color: #FFF;
  font-family: 'Oswald', sans-serif;
  font-size: 16px;
  font-weight: 300;
  text-transform: uppercase;
}

li:hover {
  color: #DBE9EE;
}

h1 {
  color: #466995;
  font-family: 'Oswald', sans-serif;
  font-size: 32px;
  font-weight: 300;
  text-transform: uppercase;
}

h2 {
  color: #333;
  font-family: 'Varela Round', sans-serif;
  font-size: 26px;
  font-weight: 100;
  margin: 0 auto 20px auto;
}

h3 {
  color: #466995;
  font-family: 'Oswald', sans-serif;
  font-size: 18px;
  text-align: center;
  font-weight: 700;
  text-transform: uppercase;
  padding: 30px;
}

h4 {
  color: #466995;
  font-family: 'Oswald', sans-serif;
  font-size: 18px;
  font-weight: 300;
  letter-spacing: 2px;
  text-align: center;
  text-transform: uppercase
}

p {
  color: #333;
  font-family: 'Varela Round', sans-serif;
  font-size: 18px;
}

footer {
  background-color: #DBE9EE;
  text-align: center;
}

.welcome {
  background-color: #DBE9EE;
  box-sizing: border-box;
  padding: 40px;
  text-align: center;
  width: 100%;
}

.question {
  text-align: center;
  position: relative;
  top: 40px;
}

.answer {
  border: 1px solid #466995;
  margin: 20px;
}

.answer:hover {
  background: #C0D6DF;
  color: #FFF;
}

标签： htmlcss

解决方案

一个流入的、不可替换的块级盒子遵守这个等式：

margin-left + border-left-width + padding-left + width + 
padding-right + border-right-width + margin-right = width of containing block

如果在您的情况下，宽度被指定为auto，则宽度被拉伸以占据所有必要的空间以使等式成立。

一个绝对定位的、不可替换的块级盒子遵守这个等式：

left + margin-left + border-left-width + padding-left + width +
padding-right + border-right-width + margin-right + right = width of containing block

首先，如果在您的情况下，left并且right是auto，宽度是包含内容所需的最小值（即它是缩小以适应），并且正确的值被拉伸以占用所有必要的空间以使等式成立.

如果您将leftand设置right为0，那么在设置width为 auto 的情况下，宽度会被拉伸以占据所有必要的空间以使等式保持不变，并且您的标题将增长到接触边框或两侧。

有关更多案例和详细信息，请参阅CSS 2.2 规范的第 10.3 节计算宽度和边距。

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