Chrome瀏覽器iPhone5視圖中的字體大小更改

這是我在桌面視圖和移動視圖中測試字體大小的代碼。我使用Chrome Inspector在桌面視圖和iphone5視圖之間切換。Chrome瀏覽器iPhone5視圖中的字體大小更改

<!DOCTYPE html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <meta http-equiv="X-UA-Compatible" content="IE=edge"> 
    <title>html5 font test</title> 
    <link rel="stylesheet" href=""> 
    <style type="text/css"> 
    body, html { 
     font-size: 18px; 
    } 
    p { 
     font-size: 1em; 
    } 
    </style> 
</head> 
<body> 
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer a arcu sed massa finibus dapibus ac sed erat. Phasellus eget magna lectus. Curabitur lectus augue, porta ac faucibus a, efficitur et mi. Phasellus id purus maximus sem placerat varius et luctus eros. Donec maximus odio at erat facilisis, id lacinia erat imperdiet. Cras lacinia orci sed nisl gravida vestibulum. Aliquam dignissim nisl ut auctor rhoncus. Nam congue, diam quis ultrices iaculis, mi purus mollis libero, sit amet egestas nulla justo vel dui. Ut pharetra bibendum lorem, eget rutrum mi scelerisque id. Nullam feugiat condimentum cursus. In at fringilla augue.</p> 

</body> 
</html>

問題是p標籤字體大小在桌面18像素，但改變成iphone5的視圖51px。當我調整瀏覽器窗口的寬度時，font-size保持爲18px，但切換到iPhone5視圖時，字體大小更改爲51px。

下面是Chrome的iPhone5的移動計算視圖字體大小