html,body,div {
    padding: 0;
    margin: 0;
}

main {
    display: flex;
    flex-direction: column;
    align-items: center;
}

input[type="text"] {
    appearance: none;
    border: unset;
    border-bottom-width: 1px;
    border-bottom-style: solid;
    border-bottom-color: black;
    box-sizing: content-box;
    transition: border .1s;
    caret-color: rgba(1, 1, 1, .3);
}
input[type="text"]:focus {
    border-bottom-width: 2px;
    outline: none;
}

.user_input {
    width: 3ch;
    text-align: center;
}

.user_input,.heading {
    font-size: 5em
}

.invalid.invalid {
    color: red;
    border-bottom-color: red;
}

.scorenote {
    visibility: hidden;
}