css的绝对定位与相对定位

.picbox{
    position: relative;
    width: 400px;
    height: 250px;
    margin: 0 auto ;

.picbox{
    position: relative;
    width: 400px;
    height: 300px;
    margin: 0 auto;

}
.picbox span{
    position: absolute;
    top:10px;
    bottom: 10px;
    color: #f3eded;
}

top:10px;
bottom: 10px;

.ttbg{
    position: absolute;
    left: 0;
    bottom: 0%;
    width: 400px;
    height: 40px;
    background: red;
    opacity: 0.1;

background:rgba(0,0,0,0.5)

position:absolute

.picbox{
    position: relative;
    width: 400px;
    height: 300px;
    margin: 0 auto;