/* --- 基础与变量定义 --- */
:root {
    /* 亮色主题：蓝绿色渐变 */
    --bg-gradient: linear-gradient(135deg, #e0f7fa 0%, #e8f5e9 100%);
    --text-color: #37474f;
    --card-bg: #ffffff;
    --card-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
    --accent-color: #00796b;
    --accent-color-light: #b2dfdb;
    --border-color: #e0e0e0;
    --header-bg: rgba(255, 255, 255, 0.8);
    --icon-color: #546e7a;
}

body.dark-mode {
    /* 暗黑主题：深蓝绿色渐变 */
    --bg-gradient: linear-gradient(135deg, #00394f 0%, #12353a 100%);
    --text-color: #cfd8dc;
    --card-bg: #1e293b;
    --card-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
    --accent-color: #4dd0e1;
    --accent-color-light: #26a69a;
    --border-color: #37474f;
    --header-bg: rgba(21, 32, 49, 0.85);
    --icon-color: #90a4ae;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background: var(--bg-gradient);
    color: var(--text-color);
    line-height: 1.7;
    transition: background 0.3s, color 0.3s;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.container {
    width: 100%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* --- 顶部导航栏 --- */
.header {
    background-color: var(--header-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 1000;
    transition: background-color 0.3s, border-color 0.3s;
}

.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    height: 64px;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-color);
    text-decoration: none;
}

.nav-menu-desktop {
    display: none; /* 移动端默认隐藏 */
    list-style: none;
    gap: 24px;
}

.nav-link {
    color: var(--text-color);
    text-decoration: none;
    font-weight: 500;
    padding: 8px 4px;
    border-bottom: 2px solid transparent;
    transition: color 0.2s, border-color 0.2s;
}

.nav-link:hover, .nav-link.active {
    color: var(--accent-color);
    border-bottom-color: var(--accent-color);
}

.nav-actions {
    display: flex;
    align-items: center;
    gap: 16px;
}

#search-input {
    padding: 8px 12px;
    border-radius: 20px;
    border: 1px solid var(--border-color);
    background-color: var(--card-bg);
    color: var(--text-color);
    transition: all 0.3s;
    width: 150px;
}
#search-input:focus {
    outline: none;
    border-color: var(--accent-color);
    width: 200px;
}

.theme-toggle-btn {
    background: none;
    border: none;
    cursor: pointer;
    width: 48px;
    height: 48px;
    display: flex;
    justify-content: center;
    align-items: center;
    color: var(--icon-color);
}
.theme-toggle-btn svg {
    width: 24px;
    height: 24px;
}
.moon-icon { display: none; }
body.dark-mode .sun-icon { display: none; }
body.dark-mode .moon-icon { display: block; }

/* --- 移动端菜单 --- */
.hamburger-btn {
    display: flex; /* 移动端默认显示 */
    flex-direction: column;
    justify-content: space-around;
    width: 24px;
    height: 24px;
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 0;
    z-index: 10;
}
.hamburger-btn span {
    width: 24px;
    height: 2px;
    background: var(--text-color);
    border-radius: 10px;
    transition: all 0.3s linear;
    position: relative;
    transform-origin: 1px;
}
.hamburger-btn.open span:nth-child(1) { transform: rotate(45deg); }
.hamburger-btn.open span:nth-child(2) { opacity: 0; transform: translateX(20px); }
.hamburger-btn.open span:nth-child(3) { transform: rotate(-45deg); }

.mobile-menu {
    display: none;
    flex-direction: column;
    position: fixed;
    top: 64px;
    left: 0;
    width: 100%;
    background-color: var(--header-bg);
    backdrop-filter: blur(10px);
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
}
.mobile-menu.open {
    display: flex;
}
.mobile-menu .nav-link {
    padding: 12px 0;
    text-align: center;
    width: 100%;
    border-bottom: 1px solid var(--border-color);
}
.mobile-menu .nav-link:last-child {
    border-bottom: none;
}

/* --- 主体内容 --- */
.main-content {
    display: flex;
    gap: 32px;
    padding-top: 32px;
    padding-bottom: 32px;
    flex-grow: 1;
}

.sidebar {
    display: none; /* 移动端默认隐藏 */
    width: 240px;
    flex-shrink: 0;
}
.sidebar h3 {
    font-size: 1.2rem;
    margin-bottom: 16px;
    color: var(--accent-color);
}
.category-list {
    list-style: none;
}
.category-list a {
    display: block;
    padding: 10px 15px;
    text-decoration: none;
    color: var(--text-color);
    border-radius: 8px;
    transition: background-color 0.2s, color 0.2s;
}
.category-list a:hover {
    background-color: var(--accent-color-light);
    color: var(--accent-color);
}
.category-list a.active {
    background-color: var(--accent-color);
    color: white;
}
body.dark-mode .category-list a.active {
    color: #00394f;
}

.notes-list {
    width: 100%;
}

.note-card {
    background-color: var(--card-bg);
    border-radius: 12px;
    padding: 24px;
    margin-bottom: 20px;
    box-shadow: var(--card-shadow);
    border: 1px solid var(--border-color);
    transition: transform 0.2s, box-shadow 0.2s;
}
.note-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 15px rgba(0, 0, 0, 0.08);
}
body.dark-mode .note-card:hover {
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.25);
}

.note-title {
    font-size: 1.5rem;
    margin-bottom: 8px;
    color: var(--accent-color);
}

.note-meta {
    display: flex;
    gap: 16px;
    font-size: 0.875rem;
    color: var(--icon-color);
    margin-bottom: 16px;
}

.note-category {
    background-color: var(--accent-color-light);
    color: var(--accent-color);
    padding: 2px 8px;
    border-radius: 12px;
    font-weight: 500;
}
body.dark-mode .note-category {
    color: #1e293b;
}

.note-excerpt {
    font-size: 1rem;
}

/* --- 页脚 --- */
.footer {
    background-color: var(--header-bg);
    padding: 20px 0;
    text-align: center;
    font-size: 0.875rem;
    color: var(--icon-color);
    border-top: 1px solid var(--border-color);
    margin-top: auto;
}
.footer a {
    color: var(--icon-color);
    text-decoration: none;
}
.footer a:hover {
    color: var(--accent-color);
}

/* --- 响应式设计断点 --- */

/* 平板 (768px) 及以上 */
@media (min-width: 768px) {
    .hamburger-btn, .mobile-menu {
        display: none; /* 隐藏汉堡菜单 */
    }
    .nav-menu-desktop {
        display: flex; /* 显示PC导航 */
    }
    .sidebar {
        display: block; /* 显示侧边栏 */
    }
}

/* PC (1200px) 及以上 */
@media (min-width: 1200px) {
    .container {
        padding: 0; /* PC端移除容器内边距 */
    }
}