css position div inside another code example

Example 1: html position div inside div

.textblock-container {
width: 500px;
height: 500px;
border: 1px solid red;
position: relative;
}

div.textblock {
width: 100px;
height: 100px;
line-height: 100px;
border: 1px solid black;
position: absolute;
text-align: center;             
background: rgb(0, 150, 0);
background: rgba(0, 150, 0, .5);
}

Example 2: all the divs from inside of another div css

#wrapper div {
    color: red;
}