18. How many columns and rows are defined in the following code?
section {
display: grid;
grid-columns: 100px 1fr 250px;
grid-rows: 50px 1fr 50px;
}
section header {
grid-column: 2;
grid-row: 1;
}
section nav {
grid-column: 1;
grid-row: 2;
}
section article {
grid-column: 2;
grid-row: 2;
}
section aside {
grid-column: 3;
grid-row: 2;
}
section footer {
grid-column: 2;
grid-row: 3;