main.css

body {
    background-color: rgb(202, 223, 160);
}

.wall {
    border: 1px solid lightgray;
    padding: 0;
    text-align: center;
    margin: 0;
    height: 1.5em;
}

.full {
    width: 30px;
}

.half {
    width: 15px;
}

.number {
    background-color: rgb(228, 43, 43);
    color: black;
    /*width: 2.2em;*/
    height: 1.5em;
    text-align: center;
    padding: 0px;
    margin: 0px;
}

.empty {
    background-color: rgb(241, 118, 118);
    color: #fff;
    padding: 0px;
    margin: 0px;
}

h1 {
    margin-top: 5px;
    margin-bottom: 5px;
}

table {
    margin-bottom: 5px;
}

.input {
    text-align: center;
    /*width: 2em;*/
    width: 100%;
    font-size: 1em;
    height: 1.5em;
    padding: 0px;
    margin: 0px;
}

/* Chrome, Safari, Edge, Opera */
input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

/* Firefox */
input[type=number] {
    -moz-appearance: textfield;
}

.correct {
    border: 3px solid green;
}

.wrong {
    border: 3px solid red;
}

.solved {
    background-color: green;
}

::-webkit-input-placeholder {
    color: #fff;
}

:-moz-placeholder {
    /* Firefox 18- */
    color: #fff;
}

::-moz-placeholder {
    /* Firefox 19+ */
    color: #fff;
}

:-ms-input-placeholder {
    color: #fff;
}


input {
    height: 1em;
    border: none;
    background: transparent;
    border-bottom: 1px solid #fff;
    outline: none;
}