为何tbody内的<td>元素无法显示为100vw宽度？

我正在学习FreeCodeCamp响应式网页设计课程，当前处于「通过制作资产负债表学习CSS伪选择器」模块第53步。尝试设置tbody内的元素宽度为100vw，预期每个的宽度等于视口宽度，但实际并未实现。

相关源代码 #

CSS代码

span[class~="sr-only"] {
  border: 0 !important;
  clip: rect(1px, 1px, 1px, 1px) !important;
  clip-path: inset(50%) !important;
  height: 1px !important;
  width: 1px !important;
  position: absolute !important;
  overflow: hidden !important;
  white-space: nowrap !important;
  padding: 0 !important;
  margin: -1px !important;
}

html {
  box-sizing: border-box;
}

body {
  font-family: sans-serif;
  color: #0a0a23;
}

h1 {
  max-width: 37.25rem;
  margin: 0 auto;
  padding: 1.5rem 1.25rem;
}

h1 .flex {
  display: flex;
  flex-direction: column-reverse;
  gap: 1rem;
}

h1 .flex span:first-of-type {
  font-size: 0.7em;
}

h1 .flex span:last-of-type {
  font-size: 1.2em;
}

section {
  max-width: 40rem;
  margin: 0 auto;
  border: 2px solid #d0d0d5;
}

#years {
  display: flex;
  justify-content: flex-end;
  position: sticky;
  z-index: 999;
  top: 0;
  background: #0a0a23;
  color: #fff;
  padding: 0.5rem calc(1.25rem + 2px) 0.5rem 0;
  margin: 0 -2px;
}

#years span[class] {
  font-weight: bold;
  width: 4.5rem;
  text-align: right;
}

.table-wrap {
  padding: 0 0.75rem 1.5rem 0.75rem;
}

span {
  font-weight: normal;
}

table {
  border-collapse: collapse;
  border: 0;
  width: 100%;
  position: relative;
  margin-top: 3rem;
}

table caption {
  color: #356eaf;
  font-size: 1.3em;
  font-weight: normal;
  position: absolute;
  top: -2.25rem;
  left: 0.5rem;
}

tbody td {
  width: 100vw;
}

HTML代码

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Balance Sheet</title>
    <link rel="stylesheet" href="./styles.css">
  </head>
  <body>
    <main>
      <section>
        <h1>
          <span class="flex">
            <span>AcmeWidgetCorp</span>
            <span>Balance Sheet</span>
          </span>
        </h1>
        <div id="years" aria-hidden="true">
          <span class="year">2019</span>
          <span class="year">2020</span>
          <span class="year">2021</span>
        </div>
        <div class="table-wrap">
          <table>
            <caption>Assets</caption>
            <thead>
              <tr>
                <td></td>
                <th><span class="sr-only year">2019</span></th>
                <th><span class="sr-only year">2020</span></th>
                <th class="current"><span class="sr-only year">2021</span></th>
              </tr>
            </thead>
            <tbody>
              <tr class="data">
                <th>Cash <span class="description">This is the cash we currently have on hand.</span></th>
                <td>$25</td>
                <td>$30</td>
                <td class="current">$28</td>
              </tr>
              <tr class="data">
                <th>Checking <span class="description">Our primary transactional account.</span></th>
                <td>$54</td>
                <td>$56</td>
                <td class="current">$53</td>
              </tr>
              <tr class="data">
                <th>Savings <span class="description">Funds set aside for emergencies.</span></th>
                <td>$500</td>
                <td>$650</td>
                <td class="current">$728</td>
              </tr>
              <tr class="total">
                <th>Total <span class="sr-only">Assets</span></th>
                <td>$579</td>
                <td>$736</td>
                <td class="current">$809</td>
              </tr>
            </tbody>
          </table>
          <table>
            <caption>Liabilities</caption>
            <thead>
              <tr>
              <td></td>
              <th><span class="sr-only">2019</span></th>
              <th><span class="sr-only">2020</span></th>
              <th><span class="sr-only">2021</span></th>
              </tr>
            </thead>
            <tbody>
              <tr class="data">
                <th>Loans <span class="description">The outstanding balance on our startup loan.</span></th>
                <td>$500</td>
                <td>$250</td>
                <td class="current">$0</td>
              </tr>
              <tr class="data">
                <th>Expenses <span class="description">Annual anticipated expenses, such as payroll.</span></th>
                <td>$200</td>
                <td>$300</td>
                <td class="current">$400</td>
              </tr>
              <tr class="data">
                <th>Credit <span class="description">The outstanding balance on our credit card.</span></th>
                <td>$50</td>
                <td>$50</td>
                <td class="current">$75</td>
              </tr>
              <tr class="total">
                <th>Total <span class="sr-only">Liabilities</span></th>
                <td>$750</td>
                <td>$600</td>
                <td class="current">$475</td>
              </tr>
            </tbody>
          </table>
          <table>
            <caption>Net Worth</caption>
            <thead>
              <tr>
              <td></td>
              <th><span class="sr-only">2019</span></th>
              <th><span class="sr-only">2020</span></th>
              <th><span class="sr-only">2021</span></th>
              </tr>
            </thead>
            <tbody>
              <tr class="total">
                <th>Total <span class="sr-only">Net Worth</span></th>
                <td>$-171</td>
                <td>$136</td>
                <td class="current">$334</td>
              </tr>
            </tbody>
          </table>
        </div>
      </section>
    </main>
  </body>
</html>

渲染效果 #

添加边框后的效果（可见宽度远小于100vw）：

原因分析 #

1. 父容器的宽度锁死：<table>被设置为width: 100%，它的宽度直接继承自父元素.table-wrap，而.table-wrap又被包裹在max-width: 40rem的<section>中，这就导致表格的最大宽度被限制在40rem内，<td>作为表格子元素，无法突破这个宽度约束。
2. 表格的布局规则限制：表格是特殊的布局容器，浏览器会自动根据列数、内容宽度分配列宽，单个<td>的width设置会被表格的布局算法覆盖，优先保证表格整体的布局合理性，不会让单个单元格独占100vw的宽度。
3. 100vw的生效条件：100vw代表视口宽度，但只有当元素的父容器没有宽度限制时，这个值才能正常生效。在表格布局中，单元格的宽度计算依赖于表格整体，而非独立的视口宽度。

可行解决方向 #

• 给<table>设置width: 100vw，突破<section>的max-width限制，但会导致表格超出容器产生横向滚动
• 修改表格的显示模式，比如给<tr>设置display: block，<td>设置display: block; width: 100vw，但这会破坏表格的默认行列结构
• 移除<section>的max-width属性，让表格可以随视口宽度自适应

内容的提问来源于stack exchange，提问作者journeywithjavascript