body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    max-width: 600px;
    margin: 2rem auto;
    padding: 20px;
    background-color: #f5f5f5;
}

@media screen and (max-width: 768px) {
    body {
        padding: 8px;
        margin: 0.5rem auto;
    }

    .calculator {
        padding: 12px;
        max-width: 100%;
    }

    h1 {
        font-size: 1.3rem;
        margin-bottom: 15px;
    }

    #shipping-options {
        display: grid;
        grid-template-columns: repeat(3, 1fr);
        gap: 6px;
        margin-bottom: 12px;
    }

    .shipping-option {
        padding: 6px 8px;
        font-size: 13px;
        text-align: center;
        margin: 0;
        border-radius: 4px;
    }

    .input-group {
        flex-direction: column;
        align-items: flex-start;
        margin-bottom: 8px;
        gap: 2px;
    }

    .input-group > label {
        margin-bottom: 2px;
        font-size: 13px;
        white-space: nowrap;
        margin-right: 0;
    }

    .input-group > input[type="number"] {
        width: 100%;
        padding: 8px;
        font-size: 13px;
        border-radius: 4px;
        min-width: 0;
    }

    .weight-input-container {
        display: grid;
        grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto;
        gap: 4px;
        width: 100%;
        align-items: center;
    }

    .weight-input-container input {
        width: 100%;
        min-width: 0;
        padding: 8px;
        font-size: 13px;
        border-radius: 4px;
    }

    .dimensions-group {
        display: flex;
        flex-direction: column;
        gap: 8px;
        margin-bottom: 12px;
    }

    .dimensions-label {
        font-size: 13px;
        color: #34495e;
        margin-bottom: 4px;
    }

    .dimensions-inputs {
        display: grid;
        grid-template-columns: repeat(3, 1fr);
        gap: 10px;
        width: 100%;
    }

    .dimensions-inputs input {
        flex: 1;
        min-width: 0;
    }

    .weight-input-container {
        display: grid;
        grid-template-columns: 1fr auto 1fr auto;
        gap: 8px;
        width: 100%;
        align-items: center;
    }

    .weight-input-container input {
        width: 100%;
        min-width: 0;
        padding: 8px;
        font-size: 13px;
        border-radius: 4px;
    }

    .weight-controls {
        display: grid;
        grid-template-columns: auto 1fr;
        gap: 8px;
        margin-top: 8px;
        align-items: center;
    }

    .button-group {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 8px;
        margin: 0;
    }

    button {
        padding: 8px;
        font-size: 13px;
        width: 100%;
        min-width: 0;
    }

    #formula-display {
        font-size: 13px;
        padding: 12px;
        line-height: 1.4;
    }

    #shipping-rules-display {
        font-size: 13px;
        padding: 12px;
    }

    .weight-tip {
        text-align: center;
        font-size: 13px;
        margin: 5px 0;
    }

    #japan-post-note {
        font-size: 13px;
        padding: 8px;
        margin: 10px 0;
        text-align: center;
    }

    #result {
        font-size: 16px;
        padding: 12px;
        margin-top: 15px;
    }
}

.version-info {
    position: fixed;
    bottom: 10px;
    right: 10px;
    background-color: rgba(0, 0, 0, 0.7);
    color: white;
    padding: 5px 10px;
    border-radius: 4px;
    font-size: 12px;
    z-index: 1000;
}

h1 {
    color: #2c3e50;
    text-align: center;
    margin-bottom: 30px;
}

.input-group {
    margin-bottom: 12px;
    display: flex;
    align-items: center;
    gap: 8px;
}

.input-group > label {
    flex: 0 0 120px;
    margin-right: 0;
    margin-bottom: 0;
}

.input-group > input[type="number"] {
    flex: 1;
}

.button-group {
    display: flex;
    gap: 10px;
    margin-top: 10px;
}

.button-group button {
    flex: 1;
}

label {
    display: block;
    margin-bottom: 8px;
    color: #34495e;
    font-weight: 500;
}

input {
    width: 100%;
    padding: 12px;
    border: 2px solid #bdc3c7;
    border-radius: 5px;
    font-size: 16px;
    box-sizing: border-box;
}

#shipping-options {
    display: flex;
    justify-content: space-around;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.shipping-option {
    padding: 8px 15px;
    border: 2px solid #ddd;
    border-radius: 5px;
    cursor: pointer;
    margin: 5px;
    transition: all 0.3s ease;
}

.shipping-option.selected {
    border-color: #3498db;
    background-color: #3498db;
    color: white;
}

button {
    background: #3498db;
    color: white;
    border: none;
    padding: 12px 25px;
    border-radius: 5px;
    cursor: pointer;
    font-size: 16px;
    transition: background 0.3s ease;
    white-space: nowrap;
    height: auto;
}

button:hover {
    background: #2980b9;
}

#result {
    margin-top: 25px;
    padding: 15px;
    border-radius: 5px;
    text-align: center;
    font-size: 18px;
    font-weight: bold;
    background: #ecf0f1;
    display: none;
}

#formula-display {
    margin-top: 20px;
    padding: 15px;
    border: 1px solid #ddd;
    border-radius: 5px;
    background-color: #f9f9f9;
    font-size: 14px;
    color: #555;
    line-height: 1.6;
    display: none;
}

#formula-display p {
    margin: 5px 0;
}

#add-extra-weight {
    padding: 8px 15px;
    font-size: 14px;
    background-color: #27ae60;
    border: none;
    color: white;
    border-radius: 4px;
    cursor: pointer;
    white-space: nowrap;
}

#add-extra-weight:hover {
    background-color: #219a52;
}

#clear-inputs {
    background-color: #e74c3c;
}

#clear-inputs:hover {
    background-color: #c0392b;
}

#japan-post-note {
    color: #e74c3c;
    font-size: 14px;
    margin-top: 10px;
    display: none;
}

#shipping-rules-display {
    margin-top: 20px;
    padding: 15px;
    background: #f8f9fa;
    border-radius: 5px;
    font-size: 14px;
    color: #7f8c8d;
}

#weight-input-group {
    flex: 1;
    margin-right: 10px;
}

.weight-input-container {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 10px;
}

.weight-controls {
    display: flex;
    align-items: center;
    gap: 15px;
}

.weight-tip {
    margin: 0;
    white-space: nowrap;
    color: #666;
    font-size: 14px;
}

.weight-input-container input {
    width: 120px;
    min-width: 0;
    margin-right: 0;
}

.weight-input-container .unit {
    flex: 0 0 auto;
    font-weight: 500;
    color: #34495e;
    padding: 0 5px;
    margin: 0 10px 0 2px;
}

#weight-g {
    flex: 1;
}