style.css

@import url('https://fonts.googleapis.com/css2?family=Roboto:wght@300;400;500;700&display=swap');

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Roboto', sans-serif;
    background: linear-gradient(135deg, #1a202c, #2d3748);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
}

button {
    outline: none;
    border: none;
    cursor: pointer;
}

button:focus {
    outline: none;
}

#previous-operand {
    word-wrap: break-word;
    word-break: break-all;
}

#current-operand {
    word-wrap: break-word;
    word-break: break-all;
}