*, *::before, *::after {
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    background: #f7f7f7;
    margin: 0;
    padding: 0 16px;
}

.container {
    max-width: 500px;
    width: 100%;
    margin: 40px auto;
    background: #fff;
    padding: 32px 24px;
    border-radius: 12px;
    box-shadow: 0 2px 16px rgba(0,0,0,0.08);
}

h1 {
    text-align: center;
    color: #333;
}

.mode-toggle {
    display: flex;
    gap: 8px;
    margin-bottom: 8px;
}

.mode-btn {
    flex: 1;
    padding: 10px;
    background: #e5e7eb;
    color: #555;
    border: 2px solid transparent;
    border-radius: 6px;
    font-size: 0.95rem;
    cursor: pointer;
    margin-bottom: 0;
    transition: background 0.2s, border-color 0.2s;
}

.mode-btn:hover {
    background: #d1d5db;
}

.mode-btn.active {
    background: #4f8cff;
    color: #fff;
    border-color: #2563eb;
}

textarea {
    width: 100%;
    min-height: 80px;
    margin: 12px 0;
    padding: 10px;
    border-radius: 6px;
    border: 1px solid #ccc;
    font-size: 1rem;
    resize: vertical;
}

button {
    width: 100%;
    padding: 12px;
    background: #4f8cff;
    color: #fff;
    border: none;
    border-radius: 6px;
    font-size: 1.1rem;
    cursor: pointer;
    margin-bottom: 16px;
    transition: background 0.2s;
}

button:hover {
    background: #2563eb;
}

#copyBtn {
    background: #22c55e;
}

#copyBtn:hover {
    background: #16a34a;
}

footer {
    text-align: center;
    color: #888;
    margin-top: 32px;
    font-size: 0.95rem;
}

footer a {
    color: #4f8cff;
    text-decoration: none;
}

footer a:hover {
    text-decoration: underline;
}

@media (max-width: 540px) {
    .container {
        margin: 20px auto;
        padding: 20px 16px;
    }

    h1 {
        font-size: 1.25rem;
    }

    button {
        font-size: 1rem;
        padding: 10px;
    }

    textarea {
        font-size: 0.95rem;
    }
}