index.css

body,
h1 {
    font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
        Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue",
        sans-serif;
    margin: 10px;
    padding: 0;
    background-color:lightslategray;
}

.container {
    align-items: center;
    text-align: center;
    max-width: 300px;
    margin: 0 auto;
    padding: 10px;
    background-color: aliceblue;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    border-radius: 5px;
    height: 450px;
}

input[type="text"] {
    width: 250px;
    height: 70px;
    margin-top: 0px;
    font-size: 35px;
    border: none;
    text-align: right;
    background: rgba(12, 12, 12, 0.1);
    border-radius: 6px;
    padding-right: 0.5rem;
    box-shadow: inset 8px 8px 8px #cbcedc;

}

button {
    cursor: pointer;
    width: 40px;
    height: 30px;
    font-size: 15px;
    border: none;
    border-radius: 6px;
    box-shadow: inset 8px 8px 8px gray;

}

.btn:hover {
    background-color: antiquewhite;
}