/* --- Global Styles & Fonts --- */
@import url('https://fonts.googleapis.com/css2?family=Montserrat:wght@400;600;700&display=swap');

:root {
    --bg-color: #1a2a33;
    --board-bg: #1f3641;
    --text-color: #a8bec9;
    --x-color: #31c3bd; /* Teal */
    --o-color: #f2b137; /* Yellow/Orange */
    --x-shadow: #118c87;
    --o-shadow: #cc8b13;
    --dark-shadow: #10212a;
    --font-family: 'Montserrat', sans-serif;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 1rem;
}

.container {
    width: 100%;
    max-width: 460px;
    text-align: center;
}

/* --- Home Screen --- */
.home-screen.active {
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

.title {
    font-size: 2.5rem;
    color: var(--text-color);
}

.subtitle {
    font-size: 1.5rem;
    color: var(--text-color);
}

.mode-selection, .difficulty-selection {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.btn {
    font-family: var(--font-family);
    font-size: 1.2rem;
    font-weight: 700;
    text-transform: uppercase;
    padding: 1rem;
    border: none;
    border-radius: 15px;
    cursor: pointer;
    transition: transform 0.2s ease;
    border-bottom: 5px solid;
}

.btn:hover {
    transform: translateY(-2px);
}

#vs-player-btn {
    background-color: var(--x-color);
    border-color: var(--x-shadow);
    color: var(--bg-color);
}

#vs-ai-btn, .difficulty-btn {
    background-color: var(--o-color);
    border-color: var(--o-shadow);
    color: var(--bg-color);
}

/* --- Main Game Screen --- */
.main-game {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.game-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.turn-indicator {
    background-color: var(--board-bg);
    padding: 0.75rem 1.5rem;
    border-radius: 10px;
    font-weight: 700;
    font-size: 1rem;
    text-transform: uppercase;
    box-shadow: inset 0 -4px 0 var(--dark-shadow);
}

.btn-restart {
    background-color: var(--text-color);
    color: var(--board-bg);
    border: none;
    width: 50px;
    height: 50px;
    border-radius: 10px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    box-shadow: inset 0 -4px 0 #6B8997;
    transition: background-color 0.2s;
}

.btn-restart:hover {
    background-color: #dbefffe0;
}

.btn-restart svg {
    stroke: var(--board-bg);
    transition: transform 0.5s ease;
}

.btn-restart:hover svg {
    transform: rotate(180deg);
}

/* --- Game Board --- */
.board-container {
    position: relative;
}

.game-board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 1.5rem;
}

.cell {
    background-color: var(--board-bg);
    width: 100%;
    aspect-ratio: 1 / 1;
    border-radius: 15px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    box-shadow: inset 0 -8px 0 var(--dark-shadow);
    transition: background-color 0.2s;
}

.cell:hover {
    background-color: #2c4a58;
}

.cell.x, .cell.o {
    cursor: not-allowed;
}

/* --- Symbol Styling --- */
.cell .symbol {
    font-size: 4rem;
    font-weight: 700;
    line-height: 1;
    animation: fadeIn 0.3s ease-in-out;
}

.cell .symbol.x { color: var(--x-color); text-shadow: 0 4px var(--x-shadow); }
.cell .symbol.o { color: var(--o-color); text-shadow: 0 4px var(--o-shadow); }

@keyframes fadeIn {
    from { opacity: 0; transform: scale(0.5); }
    to { opacity: 1; transform: scale(1); }
}

/* --- Winning Line --- */
.winning-line {
    position: absolute;
    background-color: var(--o-color);
    height: 10px;
    border-radius: 5px;
    transform-origin: center center;
    display: none; /* Hidden by default */
}


/* --- Game Over Overlay --- */
.game-over-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.7);
    display: flex;
    justify-content: center;
    align-items: center;
    opacity: 0;
    pointer-events: none;
    transition: opacity 0.3s ease;
    z-index: 100;
}

.game-over-overlay.visible {
    opacity: 1;
    pointer-events: all;
}

.overlay-content {
    background-color: var(--board-bg);
    padding: 2rem 3rem;
    border-radius: 15px;
    text-align: center;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    transform: scale(0.8);
    transition: transform 0.3s ease;
}

.game-over-overlay.visible .overlay-content {
    transform: scale(1);
}

.overlay-content h2 {
    font-size: 2rem;
    text-transform: uppercase;
    color: var(--text-color);
}

/* --- Utility Classes --- */
.hidden {
    display: none !important;
}

.active {
    display: flex !important;
}