/* 기본 스타일 초기화 */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Roboto', sans-serif;
        }

        /* 스크롤 차단 및 중앙 정렬 */
        html, body {
            height: 100%;
            overflow: hidden;
        }

        body {
            background: linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #020617 100%);
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        /* 고급스러운 글래스 카드 컨테이너 */
        .login-card {
            background: rgba(30, 41, 59, 0.45);
            backdrop-filter: blur(16px);
            -webkit-backdrop-filter: blur(16px);
            border: 1px solid rgba(255, 255, 255, 0.08);
            width: 100%;
            max-width: 420px;
            padding: 40px 35px;
            border-radius: 24px;
            box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
            animation: fadeIn 0.6s ease-out;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        /* 타이틀 섹션 */
        .login-header {
            text-align: center;
            margin-bottom: 28px;
        }

        .login-header h1 {
            font-size: 26px;
            color: #ffffff;
            font-weight: 300;
            letter-spacing: -0.5px;
        }

        .login-header h1 strong {
            color: #38bdf8;
            font-weight: 700;
        }

        .login-header p {
            color: #cbd5e1;
            font-size: 14px;
            margin-top: 6px;
        }

        /* 폼 그룹 */
        .form-group {
            margin-bottom: 20px;
        }

        .form-group label {
            display: block;
            font-size: 13px;
            color: #f1f5f9;
            font-weight: 600;
            margin-bottom: 8px;
            letter-spacing: 0.3px;
        }

        /* 입력창 디자인 */
        .form-control {
            width: 100%;
            padding: 13px 16px;
            background-color: rgba(15, 23, 42, 0.6);
            border: 1px solid #334155;
            border-radius: 12px;
            color: #ffffff;
            font-size: 15px;
            outline: none;
            transition: all 0.2s ease-in-out;
        }

        .form-control:focus {
            border-color: #38bdf8;
            box-shadow: 0 0 0 4px rgba(56, 189, 248, 0.15);
            background-color: #0f172a;
        }

        .form-control::placeholder {
            color: #64748b;
        }

        /* Captcha 컨테이너 */
        .captcha-container {
            margin-bottom: 24px;
        }

        .captcha-container .captcha-label {
            display: block;
            font-size: 13px;
            color: #f1f5f9;
            font-weight: 600;
            margin-bottom: 8px;
        }

        .captcha-flex-box {
            display: flex;
            gap: 8px;
            align-items: center;
        }

        /* [해결책 1] SimpleCaptcha 고유의 흰색 사각 모서리를 마스크처럼 강제 차단 */
        .captcha-img-wrapper {
            background-color: #ffffff; 
            border-radius: 12px;
            height: 44px;
            display: flex;
            align-items: center;
            justify-content: center;
            border: 1px solid #334155;
            flex-shrink: 0;
            overflow: hidden; /* ⭐ 중요: 내부 직사각형 이미지의 튀어나온 흰색 모서리를 완전히 잘라냅니다. */
        }

        /* [해결책 2] 강제 확대/축소를 없애고 내장 렌더링 폭을 그대로 보존 */
        #captchaImage {
            height: 100%;
            width: auto; /* 고정 width를 깨버리고 원본 비율대로 유지 */
            display: block;
            object-fit: cover;
            /* 다크모드에서 흰색 배경이 너무 쨍하다면 은은하게 녹아들도록 불투명도를 살짝 조절 가능 (선택사항) */
            opacity: 0.95; 
        }

        /* 새로고침 버튼 */
        .btn-refresh {
            width: 44px;
            height: 44px;
            background-color: rgba(15, 23, 42, 0.6);
            border: 1px solid #334155;
            color: #94a3b8;
            border-radius: 12px;
            display: flex;
            align-items: center;
            justify-content: center;
            text-decoration: none;
            transition: all 0.2s;
            cursor: pointer;
            flex-shrink: 0;
        }

        .btn-refresh:hover {
            border-color: #38bdf8;
            color: #38bdf8;
            background-color: #1e293b;
        }

        /* 캡차 입력란 */
        .captcha-input-wrapper {
            flex: 1;
        }

        /* 그라데이션 로그인 버튼 */
        .btn-submit {
            width: 100%;
            padding: 14px;
            background: linear-gradient(135deg, #38bdf8 0%, #0284c7 100%);
            color: #ffffff;
            border: none;
            border-radius: 12px;
            font-size: 16px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.25s ease;
            box-shadow: 0 4px 12px rgba(2, 132, 199, 0.3);
        }

        .btn-submit:hover {
            background: linear-gradient(135deg, #7dd3fc 0%, #0369a1 100%);
            box-shadow: 0 6px 20px rgba(2, 132, 199, 0.4);
            transform: translateY(-1px);
        }

        /* 모바일 대응 */
        @media (max-width: 480px) {
            .login-card {
                padding: 30px 20px;
            }
        }