body {
    font-family: sans-serif;
}

h1 {
    text-align: center;
}

section, div {
    display: flex;
    row-gap: 0.5em;
    column-gap: 0.5em;
    margin: 1em auto;
    justify-content: center;
    text-align: center;
    align-items: baseline;
}

.grid {
    border-spacing: 0;
    border: 1px solid black;
    border-radius: 6px;
}

.grid td, tr {
    padding: 0;
}

.grid tr:first-child td:first-child {
    border-top-left-radius: 5px;
}

.grid tr:first-child td:first-child input {
    border-top-left-radius: 4px;
}

.grid tr:first-child td:last-child {
    border-top-right-radius: 5px;
}

.grid tr:first-child td:last-child input {
    border-top-right-radius: 4px;
}

.grid tr:last-child td:first-child {
    border-bottom-left-radius: 5px;
}

.grid tr:last-child td:first-child > input {
    border-bottom-left-radius: 4px;
}

.grid tr:last-child td:last-child {
    border-bottom-right-radius: 5px;
}

.grid tr:last-child td:last-child input {
    border-bottom-right-radius: 4px;
}

.grid tr:nth-child(3n+1) td {
    border-top: 1px solid black;
}

.grid tr:nth-child(3n+2) td {
    border-top: 1px solid grey;
    border-bottom: 1px solid grey;
}

.grid tr:nth-child(3n) td {
    border-bottom: 1px solid black;
}

.grid td:nth-child(3n+1) {
    border-left: 1px solid black;
}

.grid td:nth-child(3n+2) {
    border-left: 1px solid grey;
    border-right: 1px solid grey;
}

.grid td:nth-child(3n+3) {
    border-right: 1px solid black;
}

input {
    width: 1.6em;
    height: 1.6em;
    font-size: 1.5em;
    border: 0;
    padding: 0;
    text-align: center;
    transition: background 0.5s;
}

input:enabled {
    color: darkblue;
    background: white;
}

input:disabled {
    color: white;
    background: #6666ff;
}

.same-value:enabled {
    color: #009973;
    background: #66ffd9;
}

.forbidden-value:enabled {
    background: #b3ffda;
}

.same-value:disabled {
    color: white;
    background: #00e6ac;
}

.forbidden-value:disabled {
    background: #6288ea;
}

input::placeholder {
    color: #888;
}

.buttons {
    flex-wrap: wrap;
    column-gap: 0.2em;
}

input[type="color"] {
    font-size: 1em;
    align-self: center;
}

.shortcuts caption {
    text-decoration: underline;
}

.shortcuts td {
    text-align: left;
}

kbd {
    /* from https://developer.mozilla.org */
    background-color: #eee;
    border-radius: 3px;
    border: 1px solid #b4b4b4;
    box-shadow: 0 1px 1px rgba(0,0,0,.2),0 2px 0 0 rgba(255,255,255,.7) inset;
    color: #333;
    display: inline-block;
    font-family: consolas,"Liberation Mono",courier,monospace;
    font-size: .85em;
    font-weight: 700;
    line-height: 1;
    padding: 4px;
    white-space: nowrap;
}

a {
    text-decoration: none;
}