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HomeWeb Front-endHTML Tutorial<CSS>为什么margin和top都设置为零了但是不置顶,有空隙_html/css_WEB-ITnose


就是子导航标题上面那点
<div id="head">        <ul class="ul1">            <li class="li1"><a>标题</a></li>            <li class="li1"><a>标题</a>                <div class="sonc" id="content">                    <p class="sonh">标题</p>                    <ul>                        <li class="son">标题</li>                        <li class="son">标题</li>                        <li class="son">标题</li>                        <li class="son">标题</li>                        <li class="son">标题</li>                        <li class="son">标题</li>                    </ul>                    <p class="sonh">标题</p>                    <ul>                        <li class="son">标题</li>                        <li class="son">标题</li>                        <li class="son">标题</li>                    </ul>                </div>            </li>            <li class="li1"><a>标题</a></li>        </ul>    </div>

<style>        #head{            width: 100%;            height: 80px;            background-color: rgba(193, 193, 193, 0.7);        }        ul{            list-style: none;        }        .li1{            position: relative;            float: left;            font-size: 40px;            font-weight: bold;            margin: 20px 30px 0 10px;        }        .hover1{            color: #ffffff;            border-bottom: 5px solid black;        }        .son{            font-size: 15px;            padding: 2px;            float: left;            color: black;            margin-right: 4px;            margin-top: 4px;            background-color: grey;        }        .son:hover{            background-color: #51dadd;        }        .li1 a{            text-decoration: none;        }        .sonh{            font-size: 15px;            display: inline-block;            position: relative;        }        .sonc{            border: 1px solid #a3a3a3;            height: 160px;            width: 140px;            display: none;            position: absolute;        }    </style>


回复讨论(解决方案)

*{margin:0;padding:0;}

*{margin:0;padding:0;}


没用的 而且盒子模型里已经都是0了

xhtml1.0、html4.01没有你说的问题

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">


html5的doctype才会有这个问题
<!DOCTYPE html>
把红色的去掉就好了
.sonh{
font-size: 15px;
display: inline-block;
position: relative;
}
或者把font-size:40px给li下面的a标签,不要直接给.li1

至于原因,主要是字体对行高的影响,
我的理解是 .li1的fz是40px, .sonc继承.li1的fz,
所以相对于父元素可以看成是inline元素的.sonh,它的行高自然受.sonc影响,
如果去掉.sonh的display:inline-block,
那么它作为block元素,在自定义了fz的情况下,行高就由自己决定。

以前确实没太注意html5在这里作了改变

position: relative;
是指元素 相对于未设置position:relative;状态下的位移;

以content的左上角为坐标原点,
黄色块在未position时,它的左上角相对于原点的坐标是(0,30) (你可以把两个色块的position:relative去掉看看);
所以黄色在设置了position后,它的实际坐标就是(270,30);

position: relative;
是指元素 相对于未设置position:relative;状态下的位移;

以content的左上角为坐标原点,
黄色块在未position时,它的左上角相对于原点的坐标是(0,30) (你可以把两个色块的position:relative去掉看看);
所以黄色在设置了position后,它的实际坐标就是(270,30);


那黄色块的基准为什么是(0,30) 

页面元素在未设置position:relative;前,它所占有的页面区域在那儿,在设置了position:relative;后,那个位置还是它的;

你可以把两个色块的position:relative去掉看看

页面元素在未设置position:relative;前,它所占有的页面区域在那儿,在设置了position:relative;后,那个位置还是它的;

你可以把两个色块的position:relative去掉看看


我刚才想通了 ,relitive属性元素坐标相对于的是它最原始的位置,不是父辈元素,也就是说黄色块要定位在左上角,t偏移就要设置成(0,-30),是这样吧? 能不能在问下,有什么属性是让盒子里的元素是相对盒子的起点做偏移的?

position:absolute;啊

我学傻了,一直以为absolute是脱离盒子,全局定位。relitive基于非static的父级元素,弄反了。谢大神搞清楚了

position:absolute;啊


我学傻了,一直以为absolute是脱离盒子,全局定位。relitive基于非static的父级元素,弄反了。谢大神搞清楚了 
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