@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@400;600&family=Roboto+Slab:wght@400;600&display=swap');


/* ===========================
   HW 4.2: VIEW TRANSITION STYLES
   =========================== */

@view-transition {
    navigation: auto;
}
::view-transition-old(root) {
    animation: 0.4s ease-out 0s 1 fade-out;
}
::view-transition-new(root) {
    animation: 0.4s ease-in 0s 1 fade-in;
}

@keyframes fade-in {
    from { opacity: 0; }
    to { opacity: 1; }
}
@keyframes fade-out {
    from { opacity: 1; }
    to { opacity: 0; }
}


/* ===========================
   HW 4.1: THEME VARIABLES
   =========================== */

:root {
    /* Fonts & Transitions (Static) */
    --font-main: "Poppins", "Segoe UI", sans-serif;
    --font-alt: "Roboto Slab", serif;
    --transition-fast: 0.25s ease-in-out;

    /* State Colors (Static) */
    --color-error: #d9534f;
    --color-error-shadow: rgba(217, 83, 79, 0.5);
    --color-success: #5cb85c;
    --color-warning: #f0ad4e;

    /* === Light Mode (Default) === */
    --color-accent: #4f86f7;
    --color-accent-hover: color-mix(in srgb, var(--color-accent) 80%, black);

    --color-outer-bg: #f2f6f4; /* Deleted for HW 4 */
    --color-main-bg: #f2f6f4;
    --color-card-bg: white;
    --color-sidebar-bg: #5e5a89;

    --color-text-main: #1e1e1e;
    --color-text-subtle: #888;
    --color-text-sidebar: white;
    --color-text-inverted: white;
    --color-sidebar-title: color-mix(in srgb, var(--color-accent) 50%, white);

    --color-border-soft: rgba(0, 0, 0, 0.1);
    --color-border-medium: #aaa;
    --color-border-input: #ccc;
    --color-border-form-wrapper: #ddd;

    --color-table-row-even: rgba(0, 0, 0, 0.03);
    --color-shadow-light: rgba(0, 0, 0, 0.08);
    --color-shadow-medium: rgba(0, 0, 0, 0.15);
    --color-disabled-bg: #ccc;
}

[data-theme="dark"] {
    /* === Dark Mode Overrides === */
    --color-accent-hover: color-mix(in srgb, var(--color-accent) 80%, white);

    --color-outer-bg: rgb(30, 34, 32);
    --color-main-bg: #222;
    --color-card-bg: #333;

    --color-text-main: #e0e0e0;
    --color-text-subtle: #999;

    --color-border-soft: rgba(255, 255, 255, 0.1);
    --color-border-medium: #555;
    --color-border-input: #444;
    --color-border-form-wrapper: #444;

    --color-table-row-even: rgba(255, 255, 255, 0.03);
    --color-shadow-light: rgba(0, 0, 0, 0.2);
    --color-shadow-medium: rgba(0, 0, 0, 0.3);
    --color-disabled-bg: #555;
}


/* ===========================
   BASE STYLES (Refactored)
   =========================== */

body.page {
    margin: 0;
    display: flex;
    flex-direction: row;
    min-height: 100dvh;
    background-color: var(--color-outer-bg);
    color: var(--color-text-main);
    font-family: var(--font-main);

    /* Add smooth transition for color changes */
    transition: color var(--transition-fast);
}

/* ===========================
   SIDEBAR
   =========================== */
#sidebar {
    height: 100dvh;
    position: sticky;
    top: 0;
    display: flex;
    flex-direction: column;
    flex-shrink: 0;
    width: 18%;
    min-width: 220px;
    background-color: var(--color-sidebar-bg);
    color: var(--color-text-sidebar);
    padding: 1.5rem 1.2rem;
    box-sizing: border-box;
    overflow-y: auto;
}


.sidebar-top {
    margin-bottom: 1rem;
    flex-shrink: 0;
}

.main-nav {
    flex-grow: 1;
    margin-bottom: 1rem;
}

.sidebar-bottom {
    flex-shrink: 0;
    margin-top: auto;
}

.sidebar-bottom details summary {
    cursor: pointer;
    margin-bottom: 0.5rem;
}

.sidebar-bottom .details-content {
    padding-left: 0.5rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

/* Footer字体稍微调小一点 */
#site-footer p {
    margin: 0.2rem 0;
    font-size: 0.75rem;
    opacity: 0.8;
}

.site-title {
    font-size: 1.6rem;
    font-weight: 600;
    margin-bottom: 0.3rem;
    color: var(--color-sidebar-title);
}

.site-subtitle {
    font-size: 0.85rem;
    font-weight: 400;
    margin-bottom: 1rem;
    line-height: 1.4;
}

.main-nav {
    margin-top: auto;
    flex-grow: 1;
}

/* ===========================
   MAIN CONTENT AREA (Refactored)
   =========================== */
.main-content {
    flex-grow: 1;
    background-color: var(--color-main-bg);
    padding: 3rem 4rem;
    color: var(--color-text-main);
    font-size: 1rem;
    line-height: 1.7;
    /* Deleted for HW 4
    animation: fadeIn 0.8s ease-in;*/
    min-height: 100dvh;
    box-sizing: border-box;
    overflow-x: hidden;

    /* Add smooth transition for color changes */
    transition: color var(--transition-fast);
}

.main-content h1,
.main-content h2,
.main-content h3 {
    font-family: "Roboto Slab", serif;
    color: var(--color-accent);
    margin-bottom: 0.5em;
}

.main-content p {
    margin-bottom: 1rem;
    max-width: 100%;
    white-space: normal;
}

.main-content a {
    color: var(--color-accent);
    text-decoration: none;
    border-bottom: 1px dashed var(--color-accent);
    transition: color 0.2s ease, border-color 0.2s ease;
}

.main-content a:hover {
    color: var(--color-accent-hover);
    border-color: var(--color-accent-hover);
}

.content-section {
    margin-bottom: 4rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--color-border-soft);
    transition: border-color var(--transition-fast);
}

/* ===========================
   CSS Nesting (Refactored)
   =========================== */
.nav-link {
    display: block;
    color: var(--color-text-sidebar);
    text-decoration: none;
    padding: 0.4em 0;
    font-size: 1rem;
    transition: color var(--transition-fast), transform var(--transition-fast);

    &:hover {
        color: var(--color-sidebar-title);
        transform: translateX(4px);
    }

    &.active {
        color: var(--color-accent);
        font-weight: bold;
    }
}

/* ===========================
   TABLES (Refactored)
   =========================== */
table {
    border-collapse: collapse;
    width: 100%;
    max-width: 800px;
    margin: 1rem 0;
    font-size: 0.95rem;
}

th, td {
    border: 1px solid var(--color-border-medium);
    padding: 0.6rem 1rem;
    text-align: left;
    transition: border-color var(--transition-fast);
}

th {
    background-color: color-mix(in srgb, var(--color-accent) 15%, var(--color-card-bg));
    color: var(--color-text-main);
    transition: background-color var(--transition-fast), color var(--transition-fast);
}

tr:nth-child(even) {
    background-color: var(--color-table-row-even);
    transition: background-color var(--transition-fast);
}

tr:hover {
    background-color: color-mix(in srgb, var(--color-accent) 10%, var(--color-card-bg));
    transition: background-color 0.2s ease;
}

/* ===========================
   PROJECTS GRID (Refactored)
   =========================== */
.project-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    margin-top: 2rem;
}

.project-card {
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border-soft);
    border-radius: 10px;
    padding: 1.5rem;
    box-shadow: 0 2px 4px var(--color-shadow-light);
    transition: transform 0.3s ease, box-shadow 0.3s ease,
    background-color var(--transition-fast),
    border-color var(--transition-fast);
}

.project-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 6px 12px var(--color-shadow-medium);
}

.project-card h3 {
    color: var(--color-accent);
    margin-bottom: 0.5rem;
}

.project-card p {
    font-size: 0.95rem;
    line-height: 1.5;
}

/* ===========================
   MEDIA ELEMENTS (Refactored)
   =========================== */
.experiment-figure picture,
.experiment-figure img {
    /* ... (no colors to change) ... */
}

.media-frame {
    /* ... */
    border: 1px solid var(--color-border-soft);
    box-shadow: 0 3px 6px var(--color-shadow-light);
    transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

/* ===========================
   CONTACT FORM (Refactored)
   =========================== */
form {
    background-color: var(--color-card-bg);
    border: 1px solid var(--color-border-form-wrapper);
    box-shadow: 0 3px 8px var(--color-shadow-light);
    transition: background-color var(--transition-fast),
    border-color var(--transition-fast),
    box-shadow var(--transition-fast);
    /* ... (rest of layout styles) ... */
    border-radius: 6px;
    padding: 1.2rem;
    max-width: 500px;
    margin: 1rem auto;
}

form label {
    color: var(--color-text-main);
    /* ... (rest of layout styles) ... */
    display: block;
    font-weight: 600;
    margin-top: 0.4rem;
    margin-bottom: 0.25rem;
    font-size: 0.85rem;
}

form input[type="text"],
form input[type="email"],
form textarea {
    border: 1px solid var(--color-border-input);
    background-color: var(--color-main-bg); /* Use main bg for inputs */
    color: var(--color-text-main);
    transition: border-color var(--transition-fast),
    background-color var(--transition-fast),
    color var(--transition-fast);
    /* ... (rest of layout styles) ... */
    width: 100%;
    padding: 0.35rem 0.6rem;
    border-radius: 5px;
    font-family: var(--font-main);
    font-size: 0.85rem;
    box-sizing: border-box;
    margin-bottom: 0.5rem;
}

form textarea {
    /* ... (no colors) ... */
}

.submit-btn {
    background-color: var(--color-accent);
    color: var(--color-text-inverted);
    /* ... (rest of styles) ... */
    font-weight: 600;
    letter-spacing: 0.5px;
    border: none;
    padding: 0.8rem 1.8rem;
    border-radius: 8px;
    margin-top: 1.2rem;
    cursor: pointer;
    transition: background-color var(--transition-fast),
    transform var(--transition-fast),
    box-shadow var(--transition-fast);
    align-self: flex-start;
}

.submit-btn:hover {
    background-color: var(--color-accent-hover);
    box-shadow: 0 3px 6px rgba(0,0,0,0.2);
    transform: translateY(-1px);
}

.submit-btn:disabled {
    background-color: var(--color-disabled-bg);
    cursor: not-allowed;
    box-shadow: none;
}

/* ===========================
   TIME TAG (Refactored)
   =========================== */
time {
    color: var(--color-text-subtle);
    /* ... (rest of styles) ... */
    font-size: 0.85rem;
    font-style: italic;
    letter-spacing: 0.3px;
    margin-left: 0.25rem;
    vertical-align: middle;
    display: inline-block;
    transition: color var(--transition-fast);
}
time:hover {
    color: var(--color-accent);
}

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


/* ===========================
   HW4 VALIDATION (Refactored)
   =========================== */

form .form-input:invalid:not(:placeholder-shown) {
    border-color: var(--color-error);
    box-shadow: 0 0 5px var(--color-error-shadow);
}

form .form-input:valid:not(:placeholder-shown) {
    border-color: var(--color-success);
}

#info-output.near-limit {
    color: var(--color-warning);
    font-weight: bold;
}

#info-output.over-limit {
    color: var(--color-error);
    font-weight: bold;
}

/* (Adding back the flashing error from previous step, now variable-ized) */
.flashing-error {
    border-color: var(--color-error);
    animation: flash-red 0.5s 3; /* 闪烁3次 */
}

@keyframes flash-red {
    0%, 100% {
        box-shadow: 0 0 5px var(--color-error-shadow);
    }
    50% {
        box-shadow: none;
    }
}

/* ===========================
   HW 4.1: THEME TOGGLE STYLES
   =========================== */

/* 切换按钮的容器，默认隐藏 */
.theme-toggle {
    display: none; /* 由 JS 设为 'block' 来显示 */
    margin: 1rem 0;
}

.theme-toggle label {
    font-size: 0.9rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

/* 隐藏原生的 checkbox */
.theme-toggle #theme-toggle-cb {
    display: none;
}

/* 绘制开关的 "轨道" */
.theme-toggle .toggle-track {
    display: block;
    width: 40px;
    height: 22px;
    background-color: var(--color-border-medium);
    border-radius: 20px;
    position: relative;
    transition: background-color var(--transition-fast);
}

/* 绘制开关的 "旋钮" */
.theme-toggle .toggle-knob {
    display: block;
    width: 18px;
    height: 18px;
    background-color: var(--color-card-bg);
    border-radius: 50%;
    position: absolute;
    top: 2px;
    left: 2px;
    transition: transform var(--transition-fast);
}

/* "选中" (暗色模式) 时的样式 */
.theme-toggle #theme-toggle-cb:checked + .toggle-track {
    background-color: var(--color-accent);
}

.theme-toggle #theme-toggle-cb:checked + .toggle-track .toggle-knob {
    transform: translateX(18px);
}