:root {
    /* Dark Theme (Default) */
    --bg-color: #0d1117;
    --text-color: #c9d1d9;
    --primary-color: #58a6ff;
    --accent-color: #2ea043;
    --error-color: #da3633;
    --code-bg: #161b22;
    --border-color: #30363d;
    --header-bg: rgba(22, 27, 34, 0.8);
    --container-bg: rgba(22, 27, 34, 0.8);
    --input-bg: #0d1117;
    --shadow-color: rgba(0, 0, 0, 0.5);
    --hover-bg: rgba(177, 186, 196, 0.12);
}

[data-theme="light"] {
    /* Light Theme */
    --bg-color: #f0f2f5;
    --text-color: #24292f;
    --primary-color: #0969da;
    --accent-color: #1a7f37;
    --error-color: #cf222e;
    --code-bg: #ffffff;
    --border-color: #d0d7de;
    --header-bg: rgba(255, 255, 255, 0.8);
    --container-bg: rgba(255, 255, 255, 0.8);
    --input-bg: #ffffff;
    --shadow-color: rgba(0, 0, 0, 0.1);
    --hover-bg: rgba(234, 238, 242, 0.5);
}

.icon {
    display: inline-block;
    vertical-align: text-bottom;
    fill: currentColor;
}

body {
    /* background-color: var(--bg-color); Removed to avoid conflict with transparent */
    color: var(--text-color);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji";
    margin: 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    background-color: transparent; /* For particles visibility */
    transition: color 0.3s ease;
    line-height: 1.5;
}

#particles-canvas {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    background-color: var(--bg-color);
    transition: background-color 0.3s ease;
}

header {
    background-color: var(--header-bg); /* Semi-transparent */
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

header h1 {
    font-size: 1.5rem;
    margin: 0;
    color: var(--primary-color);
    text-shadow: 0 0 10px rgba(88, 166, 255, 0.3);
}

/* User Info & Dropdown */
.user-info {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.btn-link {
    color: var(--text-color);
    text-decoration: none;
    padding: 0.25rem 0.5rem;
    border-radius: 4px;
    transition: background-color 0.2s;
}

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

.dropdown {
    position: relative;
    display: inline-block;
}

/* 隐形桥梁 - 放在父元素上，确保 hover 状态延续 */
.dropdown::after {
    content: '';
    position: absolute;
    top: 100%;
    left: 0;
    width: 100%;
    height: 15px; /* 覆盖间隙，稍微大一点确保安全 */
    background: transparent;
}

.dropdown-trigger {
    display: flex;
    align-items: center;
    cursor: pointer;
    padding: 0.25rem 0.5rem;
    border-radius: 4px;
    transition: background-color 0.2s;
}

.dropdown-trigger:hover {
    background-color: var(--hover-bg);
}

.avatar-small {
    width: 24px;
    height: 24px;
    border-radius: 50%;
    margin-right: 0.5rem;
    border: 1px solid var(--border-color);
}

.arrow {
    font-size: 0.75rem;
    margin-left: 0.5rem;
    opacity: 0.7;
}

.dropdown-menu {
    display: none;
    position: absolute;
    right: 0;
    top: 100%;
    margin-top: 10px; /* 视觉间隙 */
    background-color: var(--code-bg);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    box-shadow: 0 8px 24px var(--shadow-color);
    min-width: 160px;
    z-index: 100;
    overflow: hidden;
}

.dropdown:hover .dropdown-menu {
    display: block;
}

.dropdown-menu a {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    color: var(--text-color);
    text-decoration: none;
    transition: background-color 0.2s;
}

.dropdown-menu a:hover {
    background-color: var(--primary-color);
    color: white;
}

.dropdown-menu .divider {
    height: 1px;
    background-color: var(--border-color);
    margin: 0.25rem 0;
}

.dropdown-menu .text-danger:hover {
    background-color: var(--error-color);
}

main {
    flex: 1;
    padding: 2rem;
    max-width: 800px;
    margin: 0 auto;
    width: 100%;
    box-sizing: border-box;
}

.puzzle-container {
    background-color: var(--container-bg); /* Semi-transparent */
    backdrop-filter: blur(5px);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    padding: 2rem;
    box-shadow: 0 4px 12px var(--shadow-color);
}

.puzzle-title {
    font-size: 1.25rem;
    margin-bottom: 1.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

.puzzle-content {
    margin-bottom: 2rem;
    line-height: 1.6;
}

input[type="text"], input[type="password"] {
    background-color: var(--input-bg);
    border: 1px solid var(--border-color);
    color: var(--text-color);
    padding: 0.5rem;
    border-radius: 4px;
    width: 100%;
    box-sizing: border-box;
    font-family: inherit;
    margin-bottom: 1rem;
}

input[type="text"]:focus, input[type="password"]:focus {
    border-color: var(--primary-color);
    outline: none;
    box-shadow: 0 0 0 2px rgba(88, 166, 255, 0.3);
}

button {
    background-color: var(--accent-color);
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    cursor: pointer;
    font-family: inherit;
    font-size: 1rem;
    transition: background-color 0.2s;
}

button:hover {
    background-color: #2c974b;
}

footer {
    text-align: center;
    padding: 1rem;
    border-top: 1px solid var(--border-color);
    font-size: 0.9rem;
    color: #8b949e;
}

a {
    color: var(--primary-color);
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

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

.puzzle-container {
    animation: fadeIn 0.5s ease-out;
}

.error-message {
    color: var(--error-color);
    margin-top: 1rem;
}

/* Utility classes */
.hidden { display: none; }
.text-center { text-align: center; }
.mt-2 { margin-top: 1rem; }