W3Schools Tryit Editor

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<body>
<h2>Padding and element width - with box-sizing</h2>
<div>This div is 300px wide.</div>
<br>
<div>The width of this div remains at 300px, in spite of the 50px of total left and right padding, because of the box-sizing: border-box property.
</div>
</div><div class="naked_ctrl">
<form action="/index.cgi/contrast" method="get" name="gate">
<p><a href="http://altstyle.alfasado.net">AltStyle</a> によって変換されたページ <a href="https://www.w3schools.com/css/tryit.asp?filename=trycss_padding_width2">(->オリジナル)</a>
/ <label>アドレス: <input type="text" name="naked_post_url" value="https://www.w3schools.com/css/tryit.asp?filename=trycss_padding_width2" size="22" /></label> <label>モード: <select name="naked_post_mode">
<option value="default">デフォルト</option>
<option value="speech">音声ブラウザ</option>
<option value="ruby">ルビ付き</option>
<option value="contrast" selected="selected">配色反転</option>
<option value="larger-text">文字拡大</option>
<option value="mobile">モバイル</option>
</select>
<input type="submit" value="表示" />
</p>
</form>
</div>		
</body>
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