:root {
    --primary-color: #4A90E2;
    --primary-hover: #357ABD;
    --bg-color: #F5F7FA;
    --text-color: #333333;
    --white: #FFFFFF;
    --border-color: #E0E6ED;
    --success-color: #50E3C2;
    --error-color: #D0021B;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
    --radius: 8px;
    --font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, 'Helvetica Neue', 'Segoe UI', 'Apple SD Gothic Neo', 'Noto Sans KR', 'Malgun Gothic', 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    display: flex;
    justify-content: center;
    min-height: 100vh;
}

.container {
    width: 100%;
    max-width: 1200px;
    padding: 2rem;
    display: flex;
    flex-direction: column;
}

header {
    text-align: center;
    margin-bottom: 3rem;
}

header h1 {
    font-size: 2.5rem;
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

header p {
    color: #666;
    font-size: 1.1rem;
}

/* Controls Section */
.controls {
    text-align: center;
    margin-bottom: 2rem;
}

.controls h2 {
    font-size: 1.2rem;
    margin-bottom: 1rem;
    color: #555;
}

.persona-selector {
    display: flex;
    justify-content: center;
    gap: 1rem;
    flex-wrap: wrap;
}

.persona-btn {
    background: var(--white);
    border: 2px solid var(--border-color);
    padding: 0.75rem 1.5rem;
    border-radius: 50px;
    font-size: 1rem;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-family: var(--font-family);
}

.persona-btn:hover {
    border-color: var(--primary-color);
    color: var(--primary-color);
}

.persona-btn.active {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
    color: var(--white);
    font-weight: 600;
}

/* Converter Area */
.converter-area {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    flex: 1;
}

.card {
    background: var(--white);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    height: 500px;
}

.card-header {
    margin-bottom: 1rem;
}

.card-header label {
    font-weight: 600;
    font-size: 1.1rem;
    color: #444;
}

textarea, .output-box {
    width: 100%;
    flex: 1;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 1rem;
    font-size: 1rem;
    font-family: var(--font-family);
    resize: none;
    line-height: 1.6;
}

textarea:focus {
    outline: none;
    border-color: var(--primary-color);
}

.output-box {
    background-color: #FAFAFA;
    overflow-y: auto;
    white-space: pre-wrap;
    color: #555;
}

.card-footer {
    margin-top: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.card-footer.right-align {
    justify-content: flex-end;
    gap: 1rem;
}

#charCount {
    font-size: 0.9rem;
    color: #888;
}

/* Buttons */
.primary-btn, .secondary-btn {
    padding: 0.75rem 1.5rem;
    border-radius: var(--radius);
    border: none;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    font-family: var(--font-family);
    transition: background-color 0.2s;
}

.primary-btn {
    background-color: var(--primary-color);
    color: var(--white);
}

.primary-btn:hover {
    background-color: var(--primary-hover);
}

.secondary-btn {
    background-color: var(--bg-color);
    color: var(--text-color);
    border: 1px solid var(--border-color);
}

.secondary-btn:hover:not(:disabled) {
    background-color: #E2E8F0;
}

.secondary-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Feedback Message */
.feedback-msg {
    font-size: 0.9rem;
    opacity: 0;
    transition: opacity 0.3s;
}

.feedback-msg.success {
    color: var(--primary-color); /* Success looks good in primary blue or distinct green */
    opacity: 1;
}

.feedback-msg.error {
    color: var(--error-color);
    opacity: 1;
}

footer {
    text-align: center;
    margin-top: 3rem;
    color: #999;
    font-size: 0.9rem;
}

/* Loading Spinner */
.spinner {
    display: inline-block;
    width: 16px;
    height: 16px;
    border: 2px solid rgba(255,255,255,0.3);
    border-radius: 50%;
    border-top-color: #fff;
    animation: spin 1s ease-in-out infinite;
    margin-right: 8px;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Responsive Design */
@media (max-width: 768px) {
    .converter-area {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }

    .card {
        height: 400px;
    }

    header h1 {
        font-size: 2rem;
    }
}