html 字号 h1 h2 h3,html标题标签（<h1>，</h1> <h2>，</h2> <h3>等）的默认字体大小（以像素为单位）是什么？</h3>...
要获得实际证据，请使用默认的Mozilla Firefox样式查看html.css(171 - 237)：
h1 {
font-size: 2em;
}
h2 {
font-size: 1.5em;
}
h3 {
font-size: 1.17em;
}
h4 {
font-size: 1.00em;
}
h5 {
font-size: 0.83em;
}
h6 {
font-size: 0.67em;
}
整个css是：
h1 {
display: block;
font-size: 2em;
font-weight: bold;
margin-block-start: .67em;
margin-block-end: .67em;
}
h2,
:-moz-any(article, aside, nav, section)
h1 {
display: block;
font-size: 1.5em;
font-weight: bold;
margin-block-start: .83em;
margin-block-end: .83em;
}
h3,
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
h1 {
display: block;
font-size: 1.17em;
font-weight: bold;
margin-block-start: 1em;
margin-block-end: 1em;
}
h4,
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
h1 {
display: block;
font-size: 1.00em;
font-weight: bold;
margin-block-start: 1.33em;
margin-block-end: 1.33em;
}
h5,
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
h1 {
display: block;
font-size: 0.83em;
font-weight: bold;
margin-block-start: 1.67em;
margin-block-end: 1.67em;
}
h6,
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
:-moz-any(article, aside, nav, section)
h1 {
display: block;
font-size: 0.67em;
font-weight: bold;
margin-block-start: 2.33em;
margin-block-end: 2.33em;
}