html, 
body {
    height: 100%;
}
.split-grid {
    display: grid;
    height: 100%;
}
.gutter {
    background-color: rgb(229, 231, 235);
    background-repeat: no-repeat;
    background-position: 50%
}
.split-grid.gt600 {
    grid-template-columns: 1fr 10px 1fr;
}
.split-grid.gt600 .gutter {
    grid-row: 1/-1;
    cursor: col-resize;
    background-image: url(images/vertical.png);
    grid-column: 2;
}
.split-grid.lt600 {
    grid-template-rows: 1fr 10px 1fr;
}
.split-grid.lt600 .gutter {
    grid-column: 1/-1;
    cursor: row-resize;
    background-image: url(images/horizontal.png);
    grid-row: 2;
}