:root {
    --primary-color: #4f46e5; /* 세련된 인디고 블루 */
    --error-color: #ef4444;
    --bg-color: #f8fafc;
    --text-main: #1e293b;
    --text-muted: #64748b;
}

body {
    background-color: var(--bg-color);
    font-family: 'Inter', -apple-system, sans-serif;
    color: var(--text-main);
    margin: 0;
}

.sds-join-wrapper {
    max-width: 450px;
    margin: 60px auto;
    padding: 20px;
}

.sds-join-wrapper h1 {
    font-size: 24px;
    font-weight: 700;
    text-align: center;
    margin-bottom: 30px;
    letter-spacing: -0.5px;
}

.card {
    background: #ffffff;
    padding: 40px;
    border-radius: 16px;
    box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.05), 0 8px 10px -6px rgba(0, 0, 0, 0.05);
}

.card h2 {
    font-size: 14px;
    text-transform: uppercase;
    color: var(--text-muted);
    letter-spacing: 1px;
    margin-bottom: 25px;
    border-bottom: 1px solid #f1f5f9;
    padding-bottom: 10px;
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    font-size: 14px;
    font-weight: 600;
    margin-bottom: 8px;
}

.form-group label.required::after {
    content: ' *';
    color: var(--error-color);
}

.form-control {
    width: 100%;
    padding: 12px 16px;
    border: 1px solid #e2e8f0;
    border-radius: 8px;
    font-size: 15px;
    transition: all 0.2s;
    box-sizing: border-box;
}

.form-control:focus {
    outline: none;
    border-color: #C82D43;
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
}

.btn-container {
    display: flex;
    flex-direction: column; /* 세로 배치로 모바일 친화적 변경 */
    gap: 12px;
    margin-top: 30px;
}

.btn {
    width: 100%;
    padding: 14px;
    border-radius: 8px;
    font-weight: 600;
    cursor: pointer;
    border: none;
    transition: opacity 0.2s;
    font-size: 16px;
}

.btn-primary {
    background-color: #C82D43;
    color: white;
}

.btn-secondary {
    background-color: #f1f5f9;
    color: var(--text-muted);
}

.btn:hover {
    opacity: 0.9;
}

.desc {
    text-align: center;
    margin-top: 40px;
    font-size: 12px;
    color: var(--text-muted);
}