body {
    padding: 10px;
    font-family: '-apple-system', 'Clear Sans', 'Helvetica Neue', Arial, sans-serif;
    margin: auto;
    max-width: 500px;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    -o-user-select: none;
    user-select: none;
    font-size: 20px;
    background: #f5f5f5;
}

h1 {
    margin-top: 0px;
    margin-bottom: 10px;
    font-size: 22px;
}

h2 {
    margin-top: 0px;
    margin-bottom: 10px;
    font-size: 16px;
}

.grid {
    display: flex;
    flex-wrap: wrap;
    width: 100%;
    user-select: none;
    margin-top: 20px;
}

.cell {
    box-sizing: border-box;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: 700;
}

.number {
    cursor: pointer;
    font-weight: 500;
    border: 1px solid black;
    background: white;
}


.circle {
    position: relative;
}

.circle::before {
    content: "";
    position: absolute;
    top: 50%;
    left: 50%;
    width: 90%;
    height: 90%;
    border: 7px solid #6fbd6fa8;
    border-radius: 50%;
    transform: translate(-50%, -50%);
    box-sizing: border-box;
}

.delete {
    position: relative;
}

.delete::after {
    content: "";
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 120%;
    height: 120%;
    background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23ff0000' stroke-width='2' stroke-linecap='square' stroke-linejoin='miter'%3E%3Cline x1='18' y1='6' x2='6' y2='18' /%3E%3Cline x1='6' y1='6' x2='18' y2='18' /%3E%3C/svg%3E");
    opacity: 20%;
}

.hint {
    position: relative;
}

.hint::after {
    content: "";
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 120%;
    height: 120%;
    background: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23000fff' stroke-width='2' stroke-linecap='square' stroke-linejoin='miter'%3E%3Cline x1='18' y1='6' x2='6' y2='18' /%3E%3Cline x1='6' y1='6' x2='18' y2='18' /%3E%3C/svg%3E");
    opacity: 20%;
}


.vanswer {
    color: #aba2a2;
    border-top: 1px solid black;
}

.hanswer {
    color: #aba2a2;
    border-left: 1px solid black;
}

.correct {
    color: black;
}

.mistake {
    background-color: #ffa6a6;
}

select,
button {
    min-width: 50px;
    cursor: pointer;
    height: 50px;
    border: 2px solid black;
    font-weight: 700;
    text-align: center;
    border-radius: 10px;
    background-color: #e5e5e5;
    color: black;
    -webkit-border-radius: 10px;
    font-size: 16px;
    margin-top: 10px;
    margin-bottom: 10px;
}

select,
button:focus {
    outline: none;
}


.hidden {
    display: none;
}

.credits {
    border-top: 2px solid #e5e5e5;
    padding-top: 10px;
    margin-top: 10px;
    font-size: 16px;
    font-weight: 600;
    color: grey;
}

a {
    color: grey;
}