* {
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    background-color: #f3f4f6;
    margin: 0;
    padding: 40px 20px;
    color: #222;
}

.calculator {
    width: 100%;
    max-width: 440px;
    margin: 55px auto;
    padding: 32px;

    background-color: #ffffff;
    border: 1px solid #e1e1e1;
    border-radius: 12px;

    box-shadow: 0 5px 18px rgba(0, 0, 0, 0.08);
}

.header {
    text-align: center;
    margin-bottom: 28px;
}

.icon {
    font-size: 30px;
    margin-bottom: 8px;
}

h1 {
    margin: 0;
    font-size: 27px;
    color: #202020;
}

.header p {
    color: #707070;
    font-size: 14px;
    margin: 9px 0 0;
    line-height: 1.5;
}

label {
    display: block;
    margin-top: 17px;
    margin-bottom: 7px;

    color: #333;
    font-size: 14px;
    font-weight: 600;
}

input {
    width: 100%;
    padding: 12px;

    background-color: #fafafa;
    border: 1px solid #d1d1d1;
    border-radius: 7px;

    font-size: 15px;
    color: #222;

    outline: none;
}

input:focus {
    background-color: #fff;
    border-color: #555;
}

input::placeholder {
    color: #999;
}

button {
    width: 100%;
    margin-top: 25px;
    padding: 12px;

    background-color: #252525;
    color: white;

    border: none;
    border-radius: 7px;

    font-size: 15px;
    font-weight: 600;

    cursor: pointer;
    transition: background-color 0.2s;
}

button:hover {
    background-color: #3d3d3d;
}

button:active {
    background-color: #111;
}

#result {
    margin-top: 22px;
    padding: 16px;

    background-color: #fafafa;
    border: 1px solid #e5e5e5;
    border-radius: 7px;

    text-align: center;

    font-size: 16px;
    line-height: 1.7;
    color: #333;
}

.footer {
    margin-top: 20px;

    text-align: center;

    color: #999;
    font-size: 12px;
}

@media (max-width: 500px) {

    body {
        padding: 20px 15px;
    }

    .calculator {
        margin: 25px auto;
        padding: 25px 20px;
    }

    h1 {
        font-size: 24px;
    }
}