:root {
    /* 原有的變數 */
    --bg-color: #f0f0f0;
    --text-color: #333;
    --header-bg: rgba(240, 240, 240, 0.7);
    --header-text: black;
    --sidebar-bg: #f1f1f1;
    --sidebar-text: #000;
    --card-bg: white;
    --card-shadow: rgba(0, 0, 0, 0.1);
    --card-hover-bg: #e0e0e0;
    --footer-bg: rgb(240, 240, 240);
    --footer-text: #929292;

    /* 清華大學主題色 */
    --nthu-purple: #7E1083;
    --nthu-purple-light: #9A3B9E;
    --nthu-gold: #C89B40;
    --nthu-gold-light: #D4B26B;
}

@media (prefers-color-scheme: dark) {
    :root {
        /* 原有的暗色模式變數 */
        --bg-color: #1a1a1a;
        --text-color: #f0f0f0;
        --header-bg: rgba(26, 26, 26, 0.7);
        --header-text: #f0f0f0;
        --sidebar-bg: #2a2a2a;
        --sidebar-text: #f0f0f0;
        --card-bg: #2a2a2a;
        --card-shadow: rgba(160, 160, 160, 0.1);
        --card-hover-bg: #3a3a3a;
        --footer-bg: #1a1a1a;
        --footer-text: #929292;

        /* 暗色模式下的主題色調整 */
        --nthu-purple: hsl(297, 60%, 60%);
        --nthu-purple-light: hsl(297, 38%, 53%);
        --nthu-gold: #C89B40;
        --nthu-gold-light: hsl(41, 58%, 71%);
    }
}

body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
    background-color: var(--bg-color);
    color: var(--text-color);
}

#overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0);
    z-index: -1;
    -webkit-backdrop-filter: blur(0);
    backdrop-filter: blur(0);
    transition: all 0.3s cubic-bezier(.26, .55, .07, .98);
}

#overlay.showNavigationBar {
    background-color: rgba(0, 0, 0, 0.5);
    -webkit-backdrop-filter: blur(6px);
    backdrop-filter: blur(6px);
    z-index: 10;
}

.bodyContent {
    transition: all 0.3s cubic-bezier(.26, .55, .07, .98);
}

.bodyContent.showNavigationBar {
    z-index: inherit - 1;
}

header {
    padding: 0;
    position: relative;
    height: 250px;
    background-color: var(--header-bg);
    display: flex;
    justify-content: center;
    align-items: flex-end;
    overflow: hidden;
    transition: all 0.15s cubic-bezier(.26, .55, .07, .98);
    z-index: 1;
    -webkit-backdrop-filter: blur(20px);
    backdrop-filter: blur(20px);
    box-shadow: 0 2px 5px var(--card-shadow);
}

.sliver-bg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-image: url('cover.jpg');
    background-size: cover;
    background-position: center;
    background-color: var(--header-bg);
    filter: brightness(0.3);
    z-index: -1;
    transition: all 0.15s cubic-bezier(.26, .55, .07, .98);
}

header.sticky {
    top: -200px;
    color: var(--header-text);
    display: flex;
    position: sticky;
}

header.sticky .sliver-bg {
    height: 70%;
    opacity: 0;
    /* 背景圖片在 sticky 時淡出 */
}

.sliver-title {
    color: white;
    font-size: 2rem;
    transition: all 0.15s cubic-bezier(.26, .55, .07, .98);
    margin: 0;
    padding: 20px;
    align-content: center;
}

header.sticky .sliver-title {
    font-size: 1.25rem;
    height: 50px;
    padding: 0;
    color: var(--header-text);
}

#menu-toggle-container {
    left: 0;
    top: 0;
    display: grid;
    align-items: center;
    justify-items: center;
    position: fixed;
    background: none;
    border: none;
    height: 50px;
    width: 50px;
    z-index: 2;
    transition: all 0.15s cubic-bezier(.26, .55, .07, .98);
}

#menu-toggle {
    align-self: center;
    justify-self: center;
    position: relative;
    color: white;
    transition: all 0.15s cubic-bezier(.26, .55, .07, .98);
}

#menu-toggle.sticky {
    color: var(--header-text);
}

#sidebar {
    background-color: var(--sidebar-bg);
    padding: 1rem;
    width: 200px;
    position: fixed;
    height: 100%;
    left: -250px;
    top: 0;
    transition: all 0.3s cubic-bezier(.26, .55, .07, .98);
    z-index: 1000;
    box-shadow: 2px 0 5px rgba(0, 0, 0, 0.1);
}

#sidebar.show {
    left: 0;
}

#sidebar ul {
    list-style-type: none;
    padding: 0;
}

#sidebar ul li a {
    display: block;
    color: var(--sidebar-text);
    padding: 8px 16px;
    text-decoration: none;
}

@media (min-width: 768px) {
    #sidebar ul li a:hover {
        background-color: var(--nthu-purple);
        color: white;
    }
}


@media (max-width: 768px) {
    #sidebar ul li a {
        cursor: none;
    }
    #sidebar ul li a:active {
        background-color: var(--nthu-purple);
        color: white;
    }
}

@keyframes main {
    0% {
        opacity: 0;
        top: 20px
    }

    100% {
        opacity: 1;
        top: 0px
    }
}

main {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.cover-image {
    width: 100%;
    max-height: 400px;
    object-fit: cover;
    border-radius: 10px;
    animation-name: main;
    animation-duration: 0.5s;
}

h1, h2 {
    animation-name: main;
    animation-duration: 0.5s;
    position: relative;
}

.activity-intro {
    font-size: 1.2rem;
    line-height: 1.6;
    margin-bottom: 2rem;
    animation-name: main;
    animation-duration: 0.5s;
    position: relative;
}

.departments {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 2rem;
    animation-name: main;
    animation-duration: 0.5s;
    position: relative;
}

.department {
    background-color: var(--card-bg);
    box-shadow: 0 2px 5px var(--card-shadow);
    padding: 1.5rem;
    border-radius: 10px;
    animation-name: main;
    animation-duration: 0.5s;
    position: relative;
    overflow: hidden;
    border-left: 4px solid var(--nthu-purple);
    transition: transform 0.3s cubic-bezier(.26, .55, .07, .98);
}

.department h3 {
    color: var(--nthu-purple);
}

.timeline {
    position: relative;
    padding: 20px 0;
}

/* 基本垂直布局（窄螢幕） */
.timeline-item {
    position: relative;
    padding-left: 24px;
    margin-bottom: 32px;
}

.timeline-item:last-child {
    margin-bottom: 0;
}

.timeline-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 8px;
    bottom: -40px;
    width: 1px;
    background: linear-gradient(to right, var(--nthu-purple), var(--nthu-gold));
    opacity: 0.3;
}

.timeline-item:last-child::before {
    display: none;
}

.timeline-dot {
    position: absolute;
    left: -5px;
    top: 8px;
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--nthu-purple);
    border: 2px solid var(--nthu-gold);
}

.timeline-content {
    margin-left: 16px;
}

.timeline-time {
    font-size: 0.875rem;
    margin-bottom: 4px;
    color: var(--nthu-purple);
    font-weight: 600;
}

.timeline-title {
    font-weight: 600;
    margin-bottom: 4px;
    color: var(--text-color);
}

.timeline-description {
    font-size: 0.875rem;
    color: var(--text-color);
    opacity: 0.8;
}

/* 水平布局（寬螢幕） */
@media (min-width: 768px) {
    .timeline {
        display: flex;
        justify-content: space-between;
        padding: 40px 0;
    }

    .timeline-item {
        flex: 1;
        padding-left: 0;
        padding-top: 24px;
        margin-bottom: 0;
        margin-right: 32px;
    }

    .timeline-item:last-child {
        margin-right: 0;
    }

    .timeline-item::before {
        left: 0;
        top: 0;
        bottom: auto;
        width: 100%;
        height: 1px;
    }

    .timeline-dot {
        left: 50%;
        top: -5px;
        transform: translateX(-50%);
    }

    .timeline-content {
        margin-left: 0;
        margin-top: 16px;
        text-align: center;
    }

    .timeline-item:last-child::before {
        display: block;
    }

    .department:hover {
        transform: translateY(-5px);
        border-left: 4px solid var(--nthu-gold);
    }
    .department:hover::after {
        transform: translateX(100%);
    }
}

/* 動畫效果 */
.timeline-item {
    opacity: 0;
    transform: translateY(50px);
    animation: fadeInUp 0.5s cubic-bezier(.26, .55, .07, .98) forwards;
}

@keyframes fadeInUp {
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* 為每個項目設置不同的延遲時間 */
.timeline-item:nth-child(1) {
    animation-delay: 0.1s;
}

.timeline-item:nth-child(2) {
    animation-delay: 0.2s;
}

.timeline-item:nth-child(3) {
    animation-delay: 0.3s;
}

.timeline-item:nth-child(4) {
    animation-delay: 0.4s;
}

.contact-info {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    column-gap: 2rem;
    row-gap: 1rem;
    align-content: center;
    align-items: center;
    background-color: var(--card-bg);
    box-shadow: 0 2px 5px var(--card-shadow);
    padding: 1.5rem;
    border-radius: 10px;
    animation-name: main;
    animation-duration: 0.5s;
    position: relative;
}

.contact-info-title {
    font-weight: 900;
    color: var(--nthu-purple);
}

footer {
    background-color: var(--footer-bg);
    color: var(--footer-text);
    text-align: center;
    padding: 1rem;
    margin-top: auto;
}

@media (max-width: 800px) {
    main {
        padding: 1rem;
    }
}

@media (min-width: 800px) {
    #menu-toggle {
        cursor: pointer;
    }
}

.fa-instagram {
    /*color: #E1306C;*/
    /* Instagram's brand color */
    color: #929292;
}

.contactDetail {
    color: #929292;
    align-items: center;
    align-content: center;
}

/* 修改主要按鈕和互動元素的顏色 */
button,
.btn {
    background-color: var(--nthu-purple);
    color: white;
    transition: background-color 0.3s cubic-bezier(.26, .55, .07, .98);
}

button:hover,
.btn:hover {
    background-color: var(--nthu-purple-light);
}

/* 連結顏色修改 */
a {
    color: var(--nthu-purple);
    transition: color 0.3s cubic-bezier(.26, .55, .07, .98);
}

a:hover {
    color: var(--nthu-gold);
}
@media (min-width: 768px) {
    .timeline-item:hover .timeline-dot {
        transform: translateX(-50%) scale(1.2);
        background-color: var(--nthu-gold);
        border-color: var(--nthu-purple);
    }
}

/* 動畫效果加強 */
.timeline-dot {
    transition: all 0.3s cubic-bezier(.26, .55, .07, .98);
}

.department::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: linear-gradient(45deg, transparent, rgba(200, 155, 64, 0.1), transparent);
    transform: translateX(-100%);
    transition: transform 0.6s cubic-bezier(.26, .55, .07, .98);
}