.tank-calculator {
    max-width: 550px;
    background: #fdfdfd;
    padding: 20px;
    margin: 30px auto;
    border-radius: 12px;
    box-shadow: 0 0 10px #ccc;
    font-family: Arial, sans-serif;
}
.tank-calculator h3 {
    text-align: center;
}
.tank-calculator label {
    display: block;
    margin-bottom: 12px;
}
.tank-calculator input,
.tank-calculator select {
    padding: 6px;
    width: calc(100% - 10px);
    margin-top: 5px;
}
.tank-calculator button {
    width: 100%;
    padding: 10px;
    background-color: #0073aa;
    color: #fff;
    border: none;
    margin-top: 10px;
    cursor: pointer;
}
.tank-calculator button:hover {
    background-color: #005f8a;
}
#tank-result {
    margin-top: 15px;
    padding: 10px;
    background: #eef;
    border-radius: 6px;
}