:root {
    --background-image-url: url('https://statictuoitre.mediacdn.vn/thumb_w/640/2017/7-1512755474943.jpg');
    --primary-color: #3498db;
    --success-color: #2ecc71;
    --error-color: #e74c3c;
    --container-bg: rgba(20, 20, 30, 0.65);
    --text-color: #ecf0f1;
    --input-bg: rgba(255, 255, 255, 0.05);
    --border-color: rgba(255, 255, 255, 0.2);
}
* { margin: 0; padding: 0; box-sizing: border-box; }
body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    height: 100vh;
    display: grid;
    place-items: center;
    color: var(--text-color);
    overflow: hidden;
    position: relative;
}
body::before {
    content: '';
    position: absolute;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background: var(--background-image-url) no-repeat center center/cover;
    filter: blur(10px) brightness(0.7);
    z-index: -1;
    transform: scale(1.1);
}
.noscript-warning {
    position: fixed; top: 0; left: 0; width: 100%;
    background-color: var(--error-color); color: white; text-align: center;
    padding: 10px; z-index: 10000; font-weight: bold;
}
.auth-container {
    width: 90%;
    max-width: 420px;
    background: var(--container-bg);
    padding: 40px;
    border-radius: 20px;
    backdrop-filter: blur(15px) saturate(150%);
    border: 1px solid var(--border-color);
    box-shadow: 0 8px 32px 0 rgba(0, 0, 0, 0.37);
    transition: all 0.5s cubic-bezier(0.25, 0.8, 0.25, 1);
    animation: slideUp 0.6s ease-out;
    overflow: hidden;
}
.form-flipper {
    transition: transform 0.6s;
    transform-style: preserve-3d;
}
.form-wrapper {
    backface-visibility: hidden;
    transition: opacity 0.4s ease-in-out, transform 0.4s ease-in-out;
}
.form-wrapper.hidden {
    display: none;
}
.auth-container h1 {
    text-align: center;
    margin-bottom: 30px;
    font-weight: 600;
    letter-spacing: 1px;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
}
.input-group {
    position: relative;
    margin-bottom: 20px;
}
.input-group i {
    position: absolute;
    left: 15px;
    top: 50%;
    transform: translateY(-50%);
    color: rgba(255,255,255,0.5);
}
input {
    width: 100%;
    padding: 15px 15px 15px 45px;
    border-radius: 10px;
    border: 1px solid var(--border-color);
    background: var(--input-bg);
    color: var(--text-color);
    font-size: 16px;
    transition: all 0.3s;
}
input::placeholder { color: rgba(255, 255, 255, 0.6); }
input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 15px rgba(52, 152, 219, 0.4);
}
button {
    width: 100%;
    padding: 15px;
    border: none;
    border-radius: 10px;
    background-color: var(--primary-color);
    color: var(--text-color);
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
}
button:hover {
    background-color: #2980b9;
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(52, 152, 219, 0.3);
}
.toggle-link { text-align: center; margin-top: 25px; }
.toggle-link a { color: var(--primary-color); text-decoration: none; font-weight: bold; }
.popup {
    position: fixed; top: 0; left: 0;
    width: 100%; height: 100%;
    background-color: rgba(0, 0, 0, 0.7);
    display: flex; justify-content: center; align-items: center;
    z-index: 1000;
    backdrop-filter: blur(5px);
    opacity: 0; visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s;
}
.popup.show { opacity: 1; visibility: visible; }
.popup-content {
    background: linear-gradient(145deg, #2c3e50, #25313f);
    padding: 30px 40px;
    border-radius: 15px;
    text-align: center;
    width: 90%;
    max-width: 380px;
    border: 1px solid var(--border-color);
    box-shadow: 0 0 40px rgba(0,0,0,0.5);
    transform: scale(0.7);
    transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}
.popup.show .popup-content { transform: scale(1); }
.popup-content .icon { font-size: 3rem; margin-bottom: 15px; }
.popup-content .icon.success { color: var(--success-color); }
.popup-content .icon.error { color: var(--error-color); }
.popup-content .icon.info { color: var(--primary-color); }
.popup-content h2 { margin-bottom: 10px; }
.popup-content p { margin-top: 0; margin-bottom: 25px; line-height: 1.6; color: #bdc3c7; }
.popup-content button { width: auto; padding: 10px 35px; }
@keyframes slideUp { from { opacity: 0; transform: translateY(50px); } to { opacity: 1; transform: translateY(0); } }