* {
    box-sizing: border-box;
}
.panel {
    text-align: center;
}



#board {
    position: relative;
    height: 450px;
    width: 450px;
    margin: 50px auto 30px auto;
    overflow: hidden;
    display: grid;
    grid-auto-columns: 1fr;
    grid-auto-rows: 1fr;
    grid-gap: 10px;
}
.field {
    background-color: #78bec5;
    border-radius: 14px;
    cursor: pointer;
    color: #fff;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 2em;
    font-family: 'Arial', sans-serif;
}

.free:hover {
    background-color: #3d4250;
}
#modal {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
}
#modal__window {
    position: relative;
    top: 30%;
    width: 30%;
    margin: 0 auto;
    padding: 5px 20px 20px;
    background-color: #f8f6f6;
    text-align: center;
}
button {
    min-width: 100px;
    border: 1px solid lightgray;
    padding: 15px;
    background-color: #fff;
    font-size: 20pt;
    border-radius: 15px;
    opacity: 0.7;
}

button:hover {
    box-shadow: 2px 1px 0 rgb(0, 0, 0);
}
button:active {
    box-shadow: inset 2px 1px 0;
}

.hidden {
    display: none;
}