body {
    margin: 0px;
}
.parent {
    background-color: sandybrown;
    padding: 10px;
    margin: 10px;
    border: 1px solid black;
}
.child {
    background-color: aqua;
    height: 20px;
    border: 1px solid black;
}

.fixed {
    position: fixed;
    background-color: lightblue;
    width 100%;
    padding: 10px;
    border: 1px solid blue;
}

.top {
    top: 0px;
}
.bottom {
    bottom: 0px;
}