为何480px×859px浏览器窗口中h1与p标签内容溢出？

在480px×859px的浏览器窗口中，h1标题与p段落内容出现溢出，其他设备显示正常。推测是给h1和p设置了固定宽度导致的——之前想用text-align匹配设计稿的文本对齐和每行字数效果没成功，设固定宽度后实现了设计要求，但没法适配所有设备。

CSS代码 #

* {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

html {
  font-size: 15px;
}

/*Card Styles*/

body {
  background-color: hsl(233, 47%, 7%);
  font-family: 'Inter', sans-serif;
  font-weight: 400;
}

main {
  width: 80%;
  max-width: 900px;
  margin: 1.5em;
  background-color: hsl(244, 38%, 16%);
  display: grid;
  grid-template-columns: 1fr 1fr;
  margin: 8.5em auto;
  border-radius: 6px;
}

.first {
  background-image: url('images/image-header-desktop.jpg');
  background-color: hsl(277, 64%, 61%);
  background-blend-mode: multiply;
  order: 1;
}

.second {
  padding: 3em;
}

h1 {
  color: hsl(0, 0%, 100%);
  width: 350px;
}

h1>span {
  color: hsl(277, 64%, 61%);
}

p {
  color: hsla(0, 0%, 100%, 0.75);
  margin-top: 1em;
  width: 400px;
  font-family: 'Lexend Deca', sans-serif;
  font-weight: 400;
  line-height: 1.4;
}

dl {
  margin-top: 2em;
  display: flex;
  justify-content: space-between;
}

dl dt {
  color: hsl(0, 0%, 100%);
  font-weight: 700;
  font-size: 1.25rem;
}

dl dd {
  font-variant-caps: all-petite-caps;
  color: hsla(0, 0%, 100%, 0.6);
}


/*media query styles */

@media(max-width:480px) {
  body {
    min-height: 100vh;
    padding: 2em 1em;
  }
  main {
    width: 100%;
    grid-template-rows: 250px 1fr;
    /*height property cannot be used to adjust height of grid items only grid template rows*/
    grid-template-columns: auto;
    margin: 3em auto;
    overflow: hidden;
  }
  .first {
    background-image: url('images/image-header-mobile.jpg');
    background-color: hsl(277, 64%, 61%);
    background-blend-mode: multiply;
    background-size: cover;
    order: -1;
  }
  .second {
    padding: 1.5em;
    display: grid;
    grid-template-rows: 1fr 1fr 2fr;
  }
  h1 {
    width: 300px;
    text-align: center;
    margin: 0 auto;
  }
  p {
    width: 245px;
    text-align: center;
    line-height: 1.6;
    margin: 0 auto;
  }
  dl {
    flex-direction: column;
    gap: 1.5em;
    justify-content: center;
    align-items: center;
  }
  dl div {
    width: 71px;
    /*giving all flex items equal width to make them all align*/
  }
}

HTML代码 #

<!DOCTYPE html>
<html lang="en">
    <head>
      <meta charset="UTF-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">

      <!-- displays site properly based on user's device -->
      <link rel="icon" type="image/png" sizes="32x32" href="./images/favicon-32x32.png">
      <link rel="stylesheet" href="styles.css">

      <!--fonts styles-->
      <link rel="preconnect" href="https://fonts.googleapis.com">
      <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
      <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;700&family=Lexend+Deca&display=swap" rel="stylesheet">

      <title>Frontend Mentor | Stats preview card component</title>
    </head>
    <body>
      <main class="container">
        <div class="first">
          <!--container for background image-->
        </div>
        <div class="second">
          <h1>Get <span>insights</span> that help your business grow.</h1>
          <p>Discover the benefits of data analytics and make better decisions regarding revenue, customer experience, and overall efficiency.</p>
          <div class="stats">
            <dl>
              <div>
                <dt>10k+</dt>
                <dd>companies</dd>
              </div>
              <div>
                <dt>314</dt>
                <dd>templates</dd>
              </div>
              <div>
                <dt>12M+</dt>
                <dd>queries</dd>
              </div>
            </dl>
          </div>
        </div>
      </main>
    </body>
</html>

你的推测完全正确，固定宽度是溢出的核心原因——在480px宽的窗口中，.second容器的实际可用宽度会被内边距压缩，硬设置的固定宽度会超出容器范围导致溢出。可以用相对宽度+最大宽度的组合，既满足设计稿的每行字数要求，又能自适应不同设备：

1. 修改桌面端h1和p的样式 #

h1 {
  color: hsl(0, 0%, 100%);
  width: 100%;
  max-width: 350px;
}

p {
  color: hsla(0, 0%, 100%, 0.75);
  margin-top: 1em;
  width: 100%;
  max-width: 400px;
  font-family: 'Lexend Deca', sans-serif;
  font-weight: 400;
  line-height: 1.4;
}

2. 修改移动端媒体查询内的h1和p样式 #

h1 {
  width: 100%;
  max-width: 300px;
  text-align: center;
  margin: 0 auto;
}

p {
  width: 100%;
  max-width: 245px;
  text-align: center;
  line-height: 1.6;
  margin: 0 auto;
}

3. 优化.second的grid布局（可选） #

去掉固定的行高设置，用间距控制元素位置，避免内容溢出容器：

.second {
  padding: 1.5em;
  display: grid;
  gap: 1.5em;
}

这样设置后，元素会在容器宽度允许的情况下自适应缩放，当容器宽度小于最大限制时自动占满容器，不会出现溢出；当容器宽度足够时，保持设计要求的最大宽度，匹配每行字数效果。

内容的提问来源于stack exchange，提问作者Adebimpe Abdulhamid Eniola