*{
    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, rgb(0, 0, 0));
    border-radius: 5px;
    padding: 5px;
    width: 30px;
    height: 30px;
}

.btn-voltar {
    position: fixed;
    top: 20px;
    left: 20px;
    z-index: 1000;
}

.btn-voltar button {
    background: #5b0085;
    font-family: inherit;
    padding: 0.6em 1.3em;
    font-weight: 900;
    font-size: 18px;
    border: 3px solid black;
    border-radius: 0.4em;
    box-shadow: 0.1em 0.1em;
    cursor: pointer;
    color: white;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.btn-voltar button:hover {
    transform: translate(-0.05em, -0.05em);
    box-shadow: 0.15em 0.15em;
}

.btn-voltar button:active {
    transform: translate(0.05em, 0.05em);
    box-shadow: 0.05em 0.05em;
}

@media (max-width: 768px) {
    .btn-voltar {
        top: 10px;
        left: 10px;
    }
    
    .btn-voltar button {
        font-size: 14px;
        padding: 0.5em 1em;
    }
}

@media (max-width: 480px) {
    .btn-voltar {
        top: 5px;
        left: 5px;
    }
    
    .btn-voltar button {
        font-size: 12px;
        padding: 0.4em 0.8em;
    }
}