* {
    /*box-sizing:border-box;*/
}

.content-box {
    background-color: lightblue;
    width: 300px;
    height: 300px;
    padding:50px;
    border: 20px solid;
    margin: 20px;
    /*circle is border-radius: 100%;*/
}

.border-box {
    background-color: lightgreen;
    width: 300px;
    height: 300px;
    padding:50px;
    border: 20px solid;
    margin: 20px;
    box-sizing: border-box;
    display: inline-block;
}

.inline {
    background-color: lightcoral;
    width: 60px;
    height: 60px;
    padding: 20px;
    border: 1px solid;
    margin: 20px;
    display: inline-block;
}