:root {
    --bg-color: #F0F2F5;
    --card-bg: #FFFFFF;
    --primary: #4F46E5;
    --primary-hover: #4338ca;
    --text-main: #1F2937;
    --text-sub: #9CA3AF;
    --border-color: rgba(0, 0, 0, 0.05);
    --seat-border: rgba(255, 255, 255, 0.5);
    --disabled-bg: #E5E7EB;
    --disabled-text: #D1D5DB;
    --blackboard-bg: #E5E7EB;
    --blackboard-text: #6B7280;
    --input-bg: #F3F4F6;

    --shadow-soft: 0 4px 6px -1px rgba(0, 0, 0, 0.05),
        0 2px 4px -1px rgba(0, 0, 0, 0.03);

    --radius-seat: 12px;

    --transition-speed: 0.3s;
}

[data-theme="dark"] {
    --bg-color: #18181B;
    --card-bg: #27272A;
    --primary: #6366F1;
    --primary-hover: #818CF8;
    --text-main: #F4F4F5;
    --text-sub: #A1A1AA;
    --border-color: rgba(255, 255, 255, 0.1);
    --seat-border: rgba(255, 255, 255, 0.05);
    --disabled-bg: #3F3F46;
    --disabled-text: #52525B;
    --blackboard-bg: #2D3748;
    --blackboard-text: #A0AEC0;
    --input-bg: #3F3F46;

    --shadow-soft: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
}

#overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    z-index: 998;
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s ease;
    backdrop-filter: blur(2px);
}

#overlay.active {
    opacity: 1;
    visibility: visible;
}

* {
    box-sizing: border-box;
    outline: none;
    margin: 0;
    padding: 0;
}

body.preload,
body.preload * {
    transition: none !important;
}

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

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    -webkit-appearance: none;
    margin: 0;
}

input[type=number] {
    -moz-appearance: textfield;
}

header {
    background-color: var(--card-bg);
    height: 70px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 30px;
    border-bottom: 1px solid var(--border-color);
    position: fixed;
    top: 0;
    width: 100%;
    z-index: 1000;
    transition: background-color var(--transition-speed) ease;
}

.header-titles h1 {
    font-size: 1.25rem;
    font-weight: 800;
    letter-spacing: -0.5px;
    color: var(--text-main);
}

.header-titles p {
    font-size: 0.8rem;
    color: var(--text-sub);
    margin-top: 2px;
}

.header-controls {
    display: flex;
    gap: 10px;
}

.btn-icon {
    background: none;
    border: none;
    cursor: pointer;
    padding: 8px;
    border-radius: 50%;
    color: var(--text-main);
    transition: background-color 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn-icon:hover {
    background-color: var(--input-bg);
}

#icon-sun {
    display: none;
}

#icon-moon {
    display: block;
}

[data-theme="dark"] #icon-sun {
    display: block;
}

[data-theme="dark"] #icon-moon {
    display: none;
}

.btn-reset {
    background: none;
    border: none;
    cursor: pointer;
    font-size: 0.9rem;
    color: #EF4444;
    font-weight: 600;
    padding: 8px 16px;
    border-radius: 20px;
    transition: background-color 0.2s ease;
}

.btn-reset:hover {
    background-color: rgba(239, 68, 68, 0.1);
}

.layout {
    display: flex;
    margin-top: 70px;
    height: calc(100vh - 70px);
}

nav {
    width: 340px;
    background-color: var(--card-bg);
    padding: 30px;
    border-right: 1px solid var(--border-color);
    overflow-y: auto;
    display: flex;
    flex-direction: column;
    gap: 30px;
    box-shadow: 4px 0 20px rgba(0, 0, 0, 0.02);
    z-index: 10;
    transition: background-color var(--transition-speed) ease;
}

.nav-section {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.nav-title {
    font-size: 0.95rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--text-sub);
    font-weight: 700;
    margin-bottom: 8px;
}

.input-group {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 8px;
    background-color: var(--input-bg);
    padding: 10px 16px;
    border-radius: 12px;
    transition: background-color 0.2s ease;
}

.input-group:focus-within {
    box-shadow: 0 0 0 2px var(--primary);
}

.input-group label {
    font-size: 0.9rem;
    font-weight: 600;
    color: var(--text-main);
    white-space: nowrap;
}

.input-group input {
    border: none;
    background: transparent;
    width: 100%;
    font-size: 1rem;
    font-weight: 700;
    color: var(--text-main);
    text-align: right;
}

.input-group input::placeholder {
    color: var(--text-sub);
    font-weight: 500;
}

.toggle-row {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 4px 0;
}

.toggle-row label {
    font-weight: 600;
    color: var(--text-main);
    font-size: 0.95rem;
}

.switch {
    position: relative;
    display: inline-block;
    width: 44px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: var(--input-bg);
    transition: .3s;
    border-radius: 34px;
}

.slider:before {
    position: absolute;
    content: "";
    height: 18px;
    width: 18px;
    left: 3px;
    bottom: 3px;
    background-color: white;
    transition: .3s;
    border-radius: 50%;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

input:checked+.slider {
    background-color: var(--primary);
}

input:checked+.slider:before {
    transform: translateX(20px);
}

.mobile-only {
    display: none !important;
}

.btn-icon-only {
    display: none;
}

.btn-primary {
    background-color: var(--primary);
    color: white;
    border: none;
    padding: 14px;
    border-radius: 16px;
    font-size: 1rem;
    font-weight: 700;
    cursor: pointer;
    transition: transform 0.2s ease, background-color 0.2s ease;
    box-shadow: 0 4px 12px -2px rgba(79, 70, 229, 0.4);
    width: 100%;
    max-width: 300px;
    margin-top: 20px;
    z-index: 100;
}

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: translateY(-2px);
}

.btn-primary:active {
    transform: scale(0.98);
}

main {
    flex: 1;
    padding: 40px;
    display: flex;
    flex-direction: column;
    align-items: center;
    overflow-y: auto;
    background-color: var(--bg-color);
    transition: background-color var(--transition-speed) ease;
}

#blackboard {
    width: 100%;
    max-width: 1000px;
    padding: 10px 24px;
    background-color: var(--blackboard-bg);
    color: var(--blackboard-text);
    border-radius: 16px;
    font-size: 0.9rem;
    font-weight: 700;
    letter-spacing: 1.5px;
    text-transform: uppercase;
    text-align: center;
    transition: background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

main[data-view="teacher"] #blackboard {
    order: 2;
    margin-top: 40px;
    margin-bottom: 10px;
}
main[data-view="teacher"] #seatContainer {
    order: 1;
}

main[data-view="student"] #blackboard {
    order: 1;
    margin-top: 30px;
    margin-bottom: 20px;
}
main[data-view="student"] #seatContainer {
    order: 2;
}

#btnGenerate {
    order: 3;
}
.guide-content {
    order: 4;
}
.license-footer {
    order: 5;
}

#seatContainer {
    display: grid;
    gap: 16px;
    width: 100%;
    max-width: 1000px;
    justify-content: center;
}

.seat {
    background-color: var(--card-bg);
    border-radius: var(--radius-seat);
    aspect-ratio: 3/2;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-main);

    box-shadow: var(--shadow-soft);
    border: 1px solid var(--seat-border);

    transition: all 0.2s ease;
    cursor: pointer;
    position: relative;
    user-select: none;
}

.seat:not(.disabled):hover {
    transform: translateY(-4px);
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.2);
    border-color: var(--primary);
}

.seat.rolling {
    color: var(--text-sub);
    filter: blur(1.5px);
}

.seat.confirmed {
    border: 2px solid var(--primary);
    color: var(--primary);
    background-color: var(--card-bg);
    transform: scale(1.02);
    z-index: 1;
    box-shadow: 0 4px 12px rgba(79, 70, 229, 0.25);
}

[data-theme="dark"] .seat.confirmed {
    background-color: rgba(99, 102, 241, 0.1);
}

[data-theme="light"] .seat.confirmed {
    background-color: #F5F3FF;
}

.seat.confirmed.paired {
    font-size: 1.2rem;
}

.seat.disabled {
    background-color: var(--disabled-bg);
    box-shadow: inset 0 2px 4px 0 rgba(0, 0, 0, 0.1);
    color: var(--disabled-text);
    cursor: default;
    border: 1px solid transparent;
    cursor: pointer;
}
.seat.disabled:hover {
    transform: translateY(-4px);
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.2);
}

.seat.disabled::after {
    content: "✕";
    font-size: 1.2rem;
}

@media (max-width: 900px) {
    .mobile-only {
        display: flex !important;
    }

    main {
        padding: 20px;
    }

    .layout {
        flex-direction: column;
        height: auto;
        overflow: visible;
    }

    nav {
        position: fixed;
        bottom: 0;
        left: 0;
        width: 100%;
        height: 70vh;
        max-height: 600px;
        border-right: none;
        border-radius: 20px 20px 0 0;
        box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.15);
        transform: translateY(110%);
        transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        z-index: 999;
        visibility: visible;
    }

    nav.active {
        transform: translateY(0);
    }

    .btn-primary {
        position: fixed;
        bottom: 24px;
        right: 24px;
        width: 60px;
        height: 60px;
        border-radius: 50%;
        padding: 0;
        display: flex;
        justify-content: center;
        align-items: center;
        box-shadow: 0 4px 15px rgba(79, 70, 229, 0.4);
        margin: 0;
    }

    .btn-primary .btn-text {
        display: none;
    }

    .btn-primary .btn-icon-only {
        display: block;
        font-size: 1.5rem;
    }

    #seatContainer {
        padding-bottom: 0;
    }
    
    main[data-view="teacher"] #blackboard {
        margin-bottom: 80px; 
    }
    main[data-view="teacher"] #seatContainer {
        margin-bottom: 0;
    }
    main[data-view="student"] #blackboard {
        margin-bottom: 40px; 
    }
    main[data-view="student"] #seatContainer {
        margin-bottom: 80px; 
    }

    .seat {
        aspect-ratio: 1;
        font-size: larger;
    }

    .guide-content {
        padding: 24px 20px;
        margin-top: 40px;
    }
    
    .guide-content h2 {
        font-size: 1.2rem;
    }
}

.guide-content {
    width: 100%;
    max-width: 800px;
    margin: 60px auto 20px;
    padding: 32px 40px;
    background-color: var(--card-bg);
    border-radius: 16px;
    box-shadow: var(--shadow-soft);
    border: 1px solid var(--border-color);
    text-align: left;
    transition: background-color var(--transition-speed) ease, color var(--transition-speed) ease;
}

.guide-content h2 {
    font-size: 1.4rem;
    color: var(--primary);
    margin-bottom: 16px;
    font-weight: 800;
    letter-spacing: -0.5px;
}

.guide-content h3 {
    font-size: 1.1rem;
    color: var(--text-main);
    margin: 24px 0 12px;
    font-weight: 700;
}

.guide-content p {
    color: var(--text-sub);
    line-height: 1.6;
    font-size: 0.95rem;
    margin-bottom: 16px;
}

.guide-content ul, 
.guide-content ol {
    color: var(--text-sub);
    line-height: 1.7;
    font-size: 0.95rem;
    padding-left: 24px;
    margin-bottom: 16px;
}

.guide-content li {
    margin-bottom: 6px;
}

.guide-content strong {
    color: var(--text-main);
    font-weight: 600;
}

.license-footer {
    margin-top: 60px;
    margin-bottom: 20px;
    text-align: center;
    font-size: 0.75rem;
    color: var(--text-sub);
    opacity: 0.8;
}

.license-footer p {
    margin: 0;
    font-weight: 500;
}

.license-footer a {
    color: var(--text-sub);
    text-decoration: none;
    border-bottom: 1px dotted var(--text-sub);
    transition: color 0.2s;
}

.license-footer a:hover {
    color: var(--primary);
    border-bottom-color: var(--primary);
}