h1 {
    text-align: center;
}

.a table { 
    margin-top: 20px;
    margin-bottom: 20px;
    margin-right: auto;
    margin-left: auto;
}

.a td {
    font-family: 'Times New Roman', Times, serif;
    text-decoration: underline;
}

.a td:nth-child(odd) {
    padding-right: 12px;
    text-align: right;
}

.a td:nth-child(even) {
    padding-left: 12px;;
    text-align: left;
}

/* --------------- */

.b table {
    border-spacing: 10px;
    margin-top: 20px;
    margin-bottom: 20px;
    margin-right: auto;
    margin-left: auto;
}

.b td {
    font-size: 16px;
    width: 200px;
    height: 200px;
}

.b-left-cell {
    vertical-align: top;
}

.b-right-cell {
    vertical-align: bottom;
}

.turtle-image {
    display: block;
    margin-left: auto;
    margin-right: auto;
    width: 200px;
    height: 200px;
}

/* --------------- */

.c table {
    border: 1px solid gray;
    margin-top: 20px;
    margin-bottom: 20px;
    margin-right: auto;
    margin-left: auto;
}

.c td {
    width: 100px;
    height: 100px;
}

.red-cell {
    background-color: red;
    width: 1000px;
}

.blue-cell {
    background-color: blue;
}

.yellow-cell {
    background-color: yellow;
}

.green-cell {
    background-color: green;
}

.black-cell {
    background-color: black;
}