styles.css

body {
    font-family: Arial, sans-serif;
    font-size: 24px;
    padding: 0.5em 0.5em;
    text-align: center;
}

@media (max-width: 640px) {
    body {
        font-size: 16px;
    }
}
@media (max-width: 320px) {
    body {
        font-size: 14px;
    }
}

/* table */
table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 1em;
}

thead,
tbody td:first-child {
    font-weight:bold;
}

thead,
tbody tr:nth-child(even) {
    background: #f4f4f4;
}

tbody tr[highlight] {
    background: #e0e0e0;
}

th,
td {
    height: 2em;
    width: 6em;
    padding: 0;
    border: 0.1em solid black;
    position: relative;
}

/* icons */
.iconleft,
.iconright,
.iconrank {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
}

.iconleft {
    cursor: pointer;
    left: 0.5em;
    opacity: 0.4; 
}

.iconright {
    cursor: pointer;
    right: 0.5em;
    opacity: 0.4; 
}

.iconrank {
    left: 0.5em;
    opacity: 1; 
    cursor: default;
}

.iconleft:hover,
.iconright:hover {
    opacity: 1; 
}

/* input */
input {
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    padding: 0;
    text-align: center;
    position: absolute;
    outline: none;
    border-radius: 0;
    border: 0em solid black;
    background: inherit;
    box-sizing: border-box;
    font-family: inherit;
    font-weight: inherit;
    font-size: inherit;
    animation: blink_input_focus 0.01s;
}

input:focus {
    border: 0.1em solid black;
} 

input[pattern]:invalid {
    color: red;
}

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}

@keyframes blink_input_focus {
    0% { opacity: 0; }
    100% { opacity: 1; }
}