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

body {
    font-family: 'Helvetica Neue', Arial, 'Hiragino Kaku Gothic ProN', 'Hiragino Sans', Meiryo, sans-serif;
    background: linear-gradient(135deg, #1a1a1a 0%, #2d2d2d 100%);
    color: #ffffff;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    background: rgba(0, 0, 0, 0.8);
    border: 2px solid #ff0000;
    border-radius: 10px;
    padding: 40px;
    max-width: 800px;
    width: 100%;
    box-shadow: 0 0 30px rgba(255, 0, 0, 0.5);
}

h1 {
    color: #ff0000;
    text-align: center;
    font-size: 2.5em;
    margin-bottom: 10px;
    text-shadow: 0 0 10px rgba(255, 0, 0, 0.8);
    letter-spacing: 2px;
}

.subtitle {
    text-align: center;
    color: #ffcc00;
    font-size: 1.2em;
    margin-bottom: 30px;
    font-style: italic;
}

.input-section, .output-section {
    margin-bottom: 30px;
}

label {
    display: block;
    color: #ffcc00;
    font-size: 1.1em;
    margin-bottom: 10px;
    font-weight: bold;
}

textarea {
    width: 100%;
    padding: 15px;
    background: rgba(255, 255, 255, 0.1);
    border: 1px solid #ff0000;
    border-radius: 5px;
    color: #ffffff;
    font-size: 16px;
    resize: vertical;
    font-family: inherit;
    transition: all 0.3s ease;
}

textarea:focus {
    outline: none;
    border-color: #ffcc00;
    box-shadow: 0 0 10px rgba(255, 204, 0, 0.5);
}

textarea::placeholder {
    color: rgba(255, 255, 255, 0.5);
}

button {
    background: linear-gradient(135deg, #ff0000 0%, #cc0000 100%);
    color: #ffffff;
    border: none;
    padding: 12px 30px;
    font-size: 1.1em;
    border-radius: 5px;
    cursor: pointer;
    font-weight: bold;
    transition: all 0.3s ease;
    margin-top: 15px;
    text-transform: uppercase;
    letter-spacing: 1px;
}

button:hover {
    background: linear-gradient(135deg, #ff3333 0%, #ff0000 100%);
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(255, 0, 0, 0.5);
}

button:active {
    transform: translateY(0);
}

#convertBtn {
    display: block;
    width: 100%;
    font-size: 1.3em;
    padding: 15px;
}

#copyBtn {
    background: linear-gradient(135deg, #ffcc00 0%, #ff9900 100%);
    display: inline-block;
    width: auto;
}

#copyBtn:hover {
    background: linear-gradient(135deg, #ffdd33 0%, #ffcc00 100%);
    box-shadow: 0 5px 15px rgba(255, 204, 0, 0.5);
}

.info-section {
    background: rgba(255, 0, 0, 0.1);
    border: 1px solid rgba(255, 0, 0, 0.3);
    border-radius: 5px;
    padding: 20px;
    margin-top: 30px;
}

.info-section h2 {
    color: #ff0000;
    margin-bottom: 15px;
    font-size: 1.5em;
}

.info-section ul {
    list-style: none;
    padding-left: 0;
}

.info-section li {
    color: #cccccc;
    margin-bottom: 10px;
    padding-left: 20px;
    position: relative;
}

.info-section li:before {
    content: "▶";
    color: #ffcc00;
    position: absolute;
    left: 0;
}

/* レスポンシブ対応 */
@media (max-width: 600px) {
    .container {
        padding: 20px;
    }
    
    h1 {
        font-size: 2em;
    }
    
    button {
        font-size: 1em;
    }
}