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

html, body{
    width: 100%;
    height: 100vh;
    overflow: hidden;
}

body{
    display: flex;
    justify-content: flex-start;
    align-items: center;
    background-color:#0b1120 ;
    flex-direction: column;
    padding-top: 15px;
}
h2{
    color: white;
    margin-top: 10px;
    margin-bottom: 15px;
    font-family: Arial, sans-serif;
    transition: 0.3s ease-in-out;
}

h2:hover{
    color: #ffbd00;
}

.calculator{
    width: 90%;
    max-width: 360px;
    font-family: Arial, sans-serif;
    background-color: #212529;
    border-radius: 15px;
    overflow: hidden;
}

#display{
    width: 100%;
    padding: 10px;
    font-size: 2.5rem;
    text-align: left;
    background-color: #343a40;
    color: white;
}

.keys{
    display: grid;
    grid-template-columns: repeat(4,1fr);
    gap:10px;
    padding: 25px;
}

button{
    width: 100%;
    aspect-ratio: 1;
    border-radius: 50%;
    border: none;
    background-color: #343a40;
    color: white;
    font-size: 1.75rem;
    font-weight: bold;
    cursor: pointer;
    transition: 0.5s ease-out;
}

button:hover{
    background-color: #6c757d;
}

button:active{
    background-color: #6c757d;
}

.opr-btn{
    background-color: #ffbd00;
}

.opr-btn:hover{
    background-color: #ffbd00;
}


@media (max-width: 400px){
    .calculator{
        max-width: 100%;
    }

    #display {
        font-size: 2.2rem;
        height: 80px;
    }

    .keys{
        gap: 8px;
        padding: 15px;
    }

    button{
        font-size: 1.25rem;
    }
}