style.css

@import url('https://fonts.googleapis.com/css2?family=Kanit&family=Pixelify+Sans&display=swap');
@import url('https://fonts.googleapis.com/css2?family=Kanit&display=swap');
*{
margin: 0;
padding: 0;
box-sizing: border-box;
font-family: 'Kanit', sans-serif;
font-family: 'Pixelify Sans', 'cursive';
}
body{
    background-image: url(https://img.elo7.com.br/product/original/3EC2AD6/papel-de-parede-fisica-calculo-escolar-conta-matematica-a722-adesivo-estudo.jpg);
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 3em;
}
#calc{
    width: 400px;
    padding: .5em;
    background-color: #000000;
    color:  rgb(255,255, 255);
    display: flex;
    flex-direction: column;
    border-radius: 20px;
}
#calc h3{
    font-size: .8em;
    font-weight: 300;
    color:  rgb(255,255, 255);
    font-family: 'Kanit', sans-serif;
}
#operacoes{
    text-align: right;
    overflow-wrap: break-word;
    min-height:4.6em;
}
#atual-operacao{
    min-height: 1.6em;
    font-weight: 700;
    padding: .2em;
}
#previous-operacao{
    color: #b2b1b1;
    padding: .2em;
}
#conteiner-botao{
    display: grid;
    grid-template-columns: 1fr 1fr 1fr 1fr;
    gap: 3px;
}
#conteiner-botao button{
    border: 1px solid transparent;
    border-radius: 0;
    height: 4.5em;
    width: 90px;
    font-size: 1.1em;
    font-family: 'Kanit', sans-serif;
    background-color: rgb(255,255, 255);
    cursor: pointer;
}
#conteiner-botao button:hover{
    background-color: #bababa;
    border-color: #7b7b7b;
    color: rgb(73, 240, 1);
}
#conteiner-botao .funcoes_calc{
    background-color: #4d4d4d;
    color: rgb(255, 255,255);
}
#conteiner-botao .funcoes_calc:hover{
    background-color: #7b7b7b;
    color:rgb(73, 240, 1);
}
#conteiner-botao #igual-botao{
    grid-column: span 2;
    width:187px;
    background-color:rgb(73, 240, 1);
}