1. System/device combinations where the issue does not occur:
Physical device: iOS 26.0 (23A5318c) + iPhone 16 Pro Max
2. System/device combinations where the issue does occur:
System versions:
Physical device: iOS 26.0 (23A5330a), iOS 26.0 (23A340)
Simulator: iOS 26.0 (23A339)
Device models:
Physical device: iPhone 12
Reproducible in Safari, WKWebView, and UIWebView:
Yes
Actual behavior
In WebView (and identically in Safari):
Before the keyboard is shown, header/footer elements with position: fixed are correctly aligned with the screen viewport. Scrolling up/down works as expected.
After the keyboard appears, the visualViewport position changes.
Bug: When the keyboard is dismissed, visualViewport.offsetTop does not reset to 0. As a result, fixed header/footer elements remain misaligned:
When scrolling down, the position looks correct.
When scrolling up, the header/footer are visibly offset.
Steps to reproduce
Focus an input field → the keyboard appears
Dismiss the keyboard
Observe that visualViewport.offsetTop remains >0 (does not reset to zero)
position: fixed header/footer elements are misplaced relative to the screen
Expected behavior
After the keyboard is dismissed, visualViewport.height should return to match the layout viewport, and visualViewport.offsetTop should reset to 0.
When scrolling upward, fixed elements should remain correctly positioned within the layout viewport.
Minimal reproducible demo
A simple HTML file containing:
A header and footer with position: fixed
An input element to trigger the keyboard
<!DOCTYPE html>
<html lang="zh-CN">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />
<title>H5 吸顶吸底页面 Demo</title>
<style>
* {
margin: 0;
padding: 0;
box-sizing: border-box;
}
body {
font-family: Arial, sans-serif;
height: 2000px; /* 设置内容高度 */
background-color: #f0f8ff; /* body 背景浅蓝色 */
padding-top: 120px; /* 预留 header 高度 */
padding-bottom: 60px; /* 预留 footer 高度 */
overflow-x: hidden;
}
/* 吸顶 Header */
header {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 120px;
background-color: #ff6b6b; /* 红色 */
display: flex;
align-items: center;
justify-content: center;
color: white;
font-size: 24px;
font-weight: bold;
z-index: 1000;
}
/* 吸底 Footer */
footer {
position: fixed;
bottom: 0;
left: 0;
width: 100%;
height: 60px;
background-color: #4ecdc4; /* 青绿色 */
display: flex;
align-items: center;
justify-content: center;
color: white;
font-size: 18px;
font-weight: bold;
z-index: 1000;
}
/* 输入框样式 */
.input-container {
margin: 100px auto;
width: 80%;
max-width: 600px;
text-align: center;
}
input[type='text'] {
padding: 12px;
font-size: 16px;
border: 2px solid #ddd;
border-radius: 8px;
width: 100%;
box-sizing: border-box;
}
input[type='text']:focus {
outline: none;
border-color: #4ecdc4;
}
</style>
</head>
<body>
<!-- 吸顶 Header -->
<header>吸顶 Header (120px)</header>
<!-- 主体内容 -->
<div class="input-container">
<input type="text" placeholder="请输入内容..." />
</div>
<!-- 吸底 Footer -->
<footer>吸底 Footer (60px)</footer>
</body>
</html>
