我希望输入框和选择框看起来相同，大小相同。输入框似乎遵循CSS样式，但选择框变小了。。。
<!DOCTYPE html>
<html>
<head>
<style>
.formfld {width:200px; height:50px; margin:0; padding:0;
border:1px; border-style:solid; border-color:black;}
</style>
</head>
<body>
<input type="text" name="amount" class="formfld" value="" />
<br/>
<select name="cardtype" class="formfld">
<option value="Visa">Visa</option>
<option value="Mastercard">Mastercard</option>
</select>
</body>
</html>
因为select是默认的CSS样式box-sizing: border-box;，而input没有默认的CSS样式box-sizing: border-box;
您应该尝试此代码或添加stylebox-sizing: border-box;
<!DOCTYPE html>
<html>
<head>
<style>
.formfld {width:200px; height:50px; margin:0; padding:0;
border:1px; border-style:solid; border-color:black;box-sizing: border-box;}
</style>
</head>
<body>
<input type="text" name="amount" class="formfld" value="" />
<br/>
<select name="cardtype" class="formfld">
<option value="Visa">Visa</option>
<option value="Mastercard">Mastercard</option>
</select>
</body>
</html>