:root {
    --primary-color: #4a90e2;
    --background-color: #f4f7f9;
    --text-color: #333;
    --sidebar-bg: #fff;
    --border-color: #e0e0e0;
    --correct-char: #4caf50;
    --incorrect-char: #f44336;
    --current-char-bg: #ffeb3b;
}

body {
    font-family: 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    margin: 0;
    background-color: var(--background-color);
    color: var(--text-color);
    line-height: 1.6;
}

.app-container {
    display: flex;
    height: 100vh;
}

.sidebar {
    width: 250px;
    background-color: var(--sidebar-bg);
    border-right: 1px solid var(--border-color);
    padding: 1rem;
    overflow-y: auto;
}

.sidebar h2 {
    color: var(--primary-color);
    border-bottom: 2px solid var(--primary-color);
    padding-bottom: 0.5rem;
}

.brand-title {
    text-align: center;
    font-family: 'Georgia', serif;
    font-weight: bold;
    font-size: 2rem;
    color: #2c3e50;
    margin-bottom: 1rem;
    border-bottom: none;
}

.back-button {
    display: inline-block;
    margin-bottom: 1rem;
    padding: 8px 16px;
    background-color: #007bff;
    color: white;
    text-decoration: none;
    border-radius: 5px;
    font-size: 14px;
    transition: background-color 0.3s;
}

.back-button:hover {
    background-color: #0056b3;
    text-decoration: none;
    color: white;
}

.user-info {
    background-color: #f8f9fa;
    padding: 1rem;
    border-radius: 5px;
    margin-bottom: 1rem;
    border: 1px solid var(--border-color);
}

.user-info p {
    margin: 0 0 0.5rem 0;
    font-size: 0.9rem;
    color: var(--text-color);
}

#current-username {
    font-weight: bold;
    color: var(--primary-color);
}

#logout-button {
    background-color: #dc3545;
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 3px;
    cursor: pointer;
    font-size: 0.8rem;
    transition: background-color 0.3s;
    width: 100%;
}

#logout-button:hover {
    background-color: #c82333;
}

#lesson-nav a {
    display: block;
    color: var(--text-color);
    text-decoration: none;
    padding: 0.75rem 1rem;
    border-radius: 5px;
    margin-bottom: 0.5rem;
    transition: background-color 0.3s, color 0.3s;
}

#lesson-nav a:not(.completed):hover {
    background-color: var(--primary-color);
    color: #fff;
}

#lesson-nav a.active {
    background-color: var(--primary-color);
    color: #fff;
    font-weight: bold;
}

#lesson-nav a.completed {
    color: #999;
    background-color: #f0f0f0;
    cursor: pointer; /* Allow re-visiting completed lessons */
    text-decoration: line-through;
}

#lesson-nav a.locked {
    color: #ccc;
    background-color: #f8f8f8;
    cursor: not-allowed;
}

#lesson-nav a.locked:hover {
    color: #ccc;
    background-color: #f8f8f8;
}

.main-content {
    flex-grow: 1;
    padding: 2rem;
    overflow-y: auto;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

header h1 {
    color: var(--primary-color);
    margin: 0;
}

#reset-button {
    background-color: var(--primary-color);
    color: #fff;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 5px;
    cursor: pointer;
    font-size: 0.9rem;
    transition: background-color 0.3s;
}

#reset-button:hover {
    background-color: #3a7ac2;
}

section {
    background-color: #fff;
    padding: 1.5rem;
    border-radius: 8px;
    margin-bottom: 1.5rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}

h3 {
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
    margin-top: 0;
}

#theory-list {
    list-style: none;
    padding-left: 0;
}

#theory-list li {
    margin-bottom: 0.5rem;
}

.practice-item {
    margin-bottom: 1.5rem;
}

.practice-item h4 {
    margin-bottom: 0.5rem;
}

.practice-text {
    font-family: 'Courier New', Courier, monospace;
    font-size: 1.2rem;
    border: 1px solid var(--border-color);
    padding: 1rem;
    border-radius: 5px;
    background-color: #fdfdfd;
    white-space: pre-wrap;
    margin-bottom: 0.5rem;
}

.practice-note {
    font-style: italic;
    color: #777;
}

.typing-area {
    font-family: 'Courier New', Courier, monospace;
    font-size: 1.2rem;
    border: 1px solid var(--border-color);
    padding: 1rem;
    border-radius: 5px;
    background-color: #fff;
    line-height: 1.8;
}

.typing-area .correct {
    color: var(--correct-char);
}

.typing-area .incorrect {
    color: var(--incorrect-char);
    text-decoration: underline;
}

.typing-area .current {
    background-color: var(--current-char-bg);
    border-radius: 2px;
}

#image-section {
    text-align: center;
    margin-top: 2rem;
}

#daily-image {
    max-width: 100%;
    max-height: 400px;
    height: auto;
    border-radius: 8px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

/* Login Overlay */
#login-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.8);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

/* App container is now always visible since login is handled separately */
.app-container {
    display: flex;
}

.login-modal {
    background-color: #fff;
    padding: 2rem 3rem;
    border-radius: 10px;
    text-align: center;
    max-width: 400px;
    width: 90%;
    box-shadow: 0 5px 15px rgba(0,0,0,0.3);
}

.login-modal h2 {
    color: var(--primary-color);
    margin-bottom: 1rem;
}

.login-modal p {
    margin-bottom: 1.5rem;
    color: #666;
}

#username-input, #password-input {
    display: block;
    width: 100%;
    margin: 1rem 0;
    padding: 0.75rem;
    font-size: 1rem;
    border: 1px solid var(--border-color);
    border-radius: 5px;
    box-sizing: border-box;
}

.login-buttons {
    display: flex;
    gap: 1rem;
    margin: 1.5rem 0;
}

#login-button, #register-button {
    flex: 1;
    padding: 0.75rem 1rem;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-size: 1rem;
    transition: background-color 0.3s;
}

#login-button {
    background-color: var(--primary-color);
    color: #fff;
}

#login-button:hover {
    background-color: #3a7ac2;
}

#register-button {
    background-color: var(--correct-char);
    color: #fff;
}

#register-button:hover {
    background-color: #45a049;
}

.login-note {
    font-size: 0.9rem;
    color: #888;
    margin-top: 1rem;
}