* {
    margin: 0;
    padding: 0;
}

@font-face {
    font-family: 'DS-DIGI';
    src: url('ds_digital/DS-DIGI.TTF') format('truetype'),
        url('ds_digital/DS-DIGIB.TTF') format('truetype'),
        url('ds_digital/DS-DIGII.TTF') format('truetype'),
        url('ds_digital/DS-DIGIT.TTF') format('truetype');
}

body {
    background-image: linear-gradient(gray, black);
    background-repeat: no-repeat;
    height: 100vh;
    font-family: 'Courier New', Courier, monospace;
}

.calc {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    height: 300px;
    width: 200px;
    background-color: black;
    border-radius: 5px;
    padding: 20px;
}

.display {
    background-color: white;
    height: 40px;
    width: auto;
    word-wrap: normal;
    overflow: hidden;
    border-radius: 5px;
    font-family: 'DS-DIGI', sans-serif;
    font-size: 30px;
}

.btn {
    font: 1em sans-serif;
    color: #fff;
    background-image: linear-gradient(gray, black);
    border-radius: 5px;
    padding: 5px;
    width: 30px;
    height: 30px;
}

.btn.led {
    box-shadow: 0 0 15px 5px red;
    background-image: linear-gradient(red, darkred);
    transition: box-shadow 0.1s ease,
        background-image 0.1s ease;
}