HTML小知识点汇总（一）

1.如何让heigth:100%起效?

  有时候我们设置heigth;100%,想让当前控件铺满整个屏幕,但是很少情况下这个属性能达到我们想要的效果,这是为什么呢? 
  而根据W3C的规范，百分比的高度在设定时需要根据这个元素的父元素容器的高度。所以，如果你把一个div的高度设定为height: 50%;，而它的父元素的高度是100px，那么，这个div的高度应该是50px。 
那么,为什么没效果呢? 
  浏览器根本就不计算内容的高度，除非内容超出了视窗范围(导致滚动条出现)。或者你给整个页面设置一个绝对高度。否则，浏览器就会简单的让内容往下堆砌，页面的高度根本就无需考虑。

  因为页面并没有缺省的高度值，所以，当你让一个元素的高度设定为百分比高度时，无法根据获取父元素的高度，也就无法计算自己的高度。换句话说，父元素的高度只是一个缺省值：height: auto;。当你要求浏览器根据这样一个缺省值来计算百分比高度时，只能得到undefined的结果。也就是一个null值，浏览器不会对这个值有任何的反应。 
  解决方法就是把父级元素全部设为100%的高度,覆盖掉默认的auto

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">style</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"height: 100%;"</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">style</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"height: 100%;"</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">style</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"height: 100%;"</span>></span>
      <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">p</span>></span>
        这样这个div的高度就会100%了
      <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">p</span>></span>
    <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">div</span>></span>
  <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">body</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">html</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

2.如何使得一张图片铺满整个浏览器?

也就是图片当成整个网页的背景,那么只需要下面css就可以实现了,当然前提,父级容器高度是大于或等于整个浏览器的

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.bg</span><span class="hljs-rules" style="box-sizing: border-box;">{
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">width</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">100</span>%</span></span>;
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">height</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-number" style="box-sizing: border-box;">100</span>%</span></span>;
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> center no-repeat</span></span>;
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*使得图像最大化,可以覆盖住整个面板*/</span>
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">background-size</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> cover</span></span>;
    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/*绝对定位,否则图片不显示*/</span>
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">position</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> absolute</span></span>;
    <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">z-index</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> -<span class="hljs-number" style="box-sizing: border-box;">999</span></span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

3.如何让整个网页变成灰色?

实现下面CSS效果即可

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">html</span> <span class="hljs-rules" style="box-sizing: border-box;">{ <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">100</span>%)</span></span></span>; 
<span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-webkit-filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">100</span>%)</span></span></span>; 
<span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-moz-filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">100</span>%)</span></span></span>; 
<span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-ms-filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">100</span>%)</span></span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-o-filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">100</span>%)</span></span></span>; 
<span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">url(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"data:image/svg+xml;utf8,<svg xmlns=\"http://www.w3.org/2000/svg\"><filter id=\"grayscale\"><feColorMatrix type=\"matrix\" values=\"0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\"/></filter></svg>#grayscale"</span>)</span></span></span>; 
<span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> progid:DXImageTransform.Microsoft.<span class="hljs-function" style="box-sizing: border-box;">BasicImage(grayscale=<span class="hljs-number" style="box-sizing: border-box;">1</span>)</span></span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> gray</span></span>; <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">-webkit-filter</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> <span class="hljs-function" style="box-sizing: border-box;">grayscale(<span class="hljs-number" style="box-sizing: border-box;">1</span>)</span> </span></span></span>}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>

4.bootstrap如何做到居中?

因为block 没设定宽度是不能 margin auto 来居中的，一个简单的办法是

<code class="hljs http has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-attribute" style="box-sizing: border-box;">display</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">table</span>
<span class="hljs-attribute" style="box-sizing: border-box;">width</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">auto</span>
<span class="hljs-attribute" style="box-sizing: border-box;">margin-left</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">auto</span>
<span class="hljs-attribute" style="box-sizing: border-box;">margin-right</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">auto</span>
</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

或者直接从center标签

<code class="hljs xml has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">center</span>></span>
     <span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"><<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span> <span class="hljs-attribute" style="box-sizing: border-box; color: rgb(102, 0, 102);">class</span>=<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 136, 0);">"btn btn-success btn-lg btn-store"</span>></span>立即选择<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">button</span>></span>
<span class="hljs-tag" style="color: rgb(0, 102, 102); box-sizing: border-box;"></<span class="hljs-title" style="box-sizing: border-box; color: rgb(0, 0, 136);">center</span>></span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>

再或者指定class为center-block

<code class="hljs css has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.center-block</span> <span class="hljs-rules" style="box-sizing: border-box;">{
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">display</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> block</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">margin-left</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> auto</span></span>;
  <span class="hljs-rule" style="box-sizing: border-box;"><span class="hljs-attribute" style="box-sizing: border-box;">margin-right</span>:<span class="hljs-value" style="box-sizing: border-box; color: rgb(0, 102, 102);"> auto</span></span>;
<span class="hljs-rule" style="box-sizing: border-box;">}</span></span></code>