小记录

1 div1/span在div2中水平垂直居中

　　【外层相对定位，里层绝对定位后，里层元素水平居中：left:50%;margin-left:-里层元素宽度/2; 垂直居中:top:50%;margin-top:-里层元素高度/2; magin值均为负值。】

.wai{
    width: 200px;
    height: 200px;
    box-sizing: border-box;
    border: 2px solid black;
    
    position: relative;
    left: 230px;
}


.wai .li{
    width: 150px;
    height: 150px;
    border: 2px solid lightcoral;
    box-sizing: border-box;
    
    position: absolute;
    top: 50%;
    margin-top: -75px;
    left: 50%;
    margin-left: -75px;
}

.wai2{
    width: 200px;
    height: 200px;
    box-sizing: border-box;
    border: 2px solid black;
    text-align: center;


    line-height: 200px;
}

.wai2 span{
    width: 150px;
    height: 150px;
    border: 2px solid lightcoral;
    box-sizing: border-box;
}

2 遇到的下拉列表select右边下拉箭头问题

　　【用appearance属性。appearance: none;表示不显示下拉箭头】

/*默认下拉列表select样式*/
.s1{
    width: 170px;
    height: 30px;
}

/*修改后*/
.s2{
    width: 170px;
    height: 30px;
    
    appearance: none;
    -moz-appearance: none;
    -webkit-appearance: none;
    background: url(../img/read.gif) no-repeat scroll right center transparent;
    padding-right: 10px;
}

/*进行选择时不显示默认的外围线*/
.s2:focus{
    outline: none;
}

3 圆角border-radius闲着没事练习

<div id="circle600">
    <div class="xiaobai"></div>
    <div class="xiaohei xiaobai"></div>
</div>

#circle600{
    width: 300px;
    height: 600px;
    border: 2px solid black;
    border-right: 298px solid black;
    border-radius: 300px;
}


#circle600 .xiaobai{
    width: 100px;
    height: 100px;
    background-color: black;
    border: 100px solid white;
    border-radius: 150px;
    margin-left: 150px;
    float: left;
}
#circle600 .xiaohei{
    background-color: white;
    border: 100px solid black;
}