:root {
    /* "Cosmic" Color Palette */
    --gradient-start: #2E0854; /* Deep Purple */
    --gradient-end: #480562; /* Royal Purple */
    --board-bg: rgba(255, 255, 255, 0.1);
    --cell-bg: rgba(255, 255, 255, 0.15);
    --cell-hover-bg: rgba(255, 255, 255, 0.25);
    --text-color: #f0f0f0;
    --shadow-color: rgba(0, 0, 0, 0.3);
    
    /* Vibrant Neon-like colors for X and O */
    --x-color: #F022A8; /* Electric Pink */
    --o-color: #0ABCF9; /* Bright Cyan */
    --glow-color: rgba(255, 255, 255, 0.7);
}

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

body {
    font-family: 'Poppins', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    background-attachment: fixed;
    color: var(--text-color);
    overflow: hidden;
}

.title {
    font-size: 4.5rem;
    font-weight: 700;
    text-shadow: 0 0 10px var(--glow-color), 0 0 20px var(--shadow-color);
    animation: fadeInDown 1s ease-in-out;
    letter-spacing: 2px;
}

button {
    transition: transform 0.3s ease, background-color 0.3s ease, box-shadow 0.3s ease;
}

/* --- Welcome Screen --- */
.welcome-screen {
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2rem;
    transition: opacity 0.5s ease-out, transform 0.5s ease-out;
}

.mode-selection button, #start-game-btn {
    padding: 1rem 2.5rem;
    font-size: 1.2rem;
    font-weight: 600;
    margin: 0 0.5rem;
    border: 1px solid rgba(255, 255, 255, 0.3);
    border-radius: 50px;
    cursor: pointer;
    background: var(--board-bg);
    color: var(--text-color);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    box-shadow: 0 4px 20px var(--shadow-color);
}

.mode-selection button:hover, #start-game-btn:hover {
    transform: translateY(-5px) scale(1.05);
    background: rgba(255, 255, 255, 0.2);
    box-shadow: 0 0 15px var(--glow-color), 0 6px 25px var(--shadow-color);
}

.name-inputs input {
    padding: 0.8rem;
    border-radius: 10px;
    border: 1px solid rgba(255, 255, 255, 0.4);
    background: rgba(0, 0, 0, 0.2);
    backdrop-filter: blur(5px);
    font-size: 1rem;
    color: var(--text-color);
    text-align: center;
    transition: box-shadow 0.3s ease;
}

.name-inputs input:focus {
    outline: none;
    box-shadow: 0 0 10px var(--o-color);
}

.name-inputs input::placeholder {
    color: rgba(255, 255, 255, 0.6);
}

/* --- Game Container & Scoreboard --- */
.game-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2rem;
    transition: opacity 0.5s ease-in, transform 0.5s ease-in;
}

.scoreboard-card {
    display: flex;
    justify-content: space-around;
    align-items: center;
    width: 100%;
    background: var(--board-bg);
    padding: 1.2rem 2rem;
    border-radius: 20px;
    border: 1px solid rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    box-shadow: 0 8px 32px 0 var(--shadow-color);
    animation: fadeInUp 0.5s ease-out;
}

.score-item {
    font-size: 1.3rem;
    font-weight: 600;
    padding: 0.5rem 1rem;
    border-radius: 15px;
    transition: transform 0.4s ease, box-shadow 0.4s ease, background-color 0.4s ease;
}

.turn-indicator {
    margin-top: 1rem;
    font-size: 1.6rem;
    font-weight: 600;
    text-shadow: 0 0 5px var(--glow-color);
    animation: fadeIn 1s;
}

.active-player {
    transform: scale(1.1);
    background-color: rgba(255, 255, 255, 0.15);
    box-shadow: 0 0 15px var(--glow-color);
}
.active-player span#player1-name { color: var(--x-color); }
.active-player span#player2-name { color: var(--o-color); }

/* --- Board & Cells --- */
.board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 12px;
    width: clamp(300px, 90vw, 450px);
    height: clamp(300px, 90vw, 450px);
    background: transparent;
    padding: 12px;
    border-radius: 25px;
    border: 1px solid rgba(255, 255, 255, 0.2);
    background: var(--board-bg);
    backdrop-filter: blur(12px);
    box-shadow: 0 8px 40px var(--shadow-color);
    animation: zoomIn 0.7s ease-out;
}

.cell {
    position: relative; /* Crucial for positioning the marks inside */
    background: var(--cell-bg);
    border-radius: 20px;
    display: flex;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

.cell:hover {
    background-color: var(--cell-hover-bg);
}

/* --- New Architecture for Marks --- */

/* 1. Create containers for BOTH 'X' and 'O' in every cell from the start */
.cell::before,
.cell::after {
    position: absolute; /* Take them out of the layout flow */
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);

    font-size: clamp(2.5rem, 15vw, 5rem);
    font-weight: 700;
    
    /* 2. Make them invisible by default */
    opacity: 0;
    transition: opacity 0.4s ease;
}

/* 3. Define the content and style for each mark */
.cell::before {
    content: 'X';
    color: var(--x-color);
    text-shadow: 0 0 15px var(--x-color);
}

.cell::after {
    content: 'O';
    color: var(--o-color);
    text-shadow: 0 0 15px var(--o-color);
}

/* 4. When a class is added, simply make the correct pre-existing mark visible */
.cell.x::before {
    opacity: 1;
}

.cell.o::after {
    opacity: 1;
}

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

.winning-cell {
    animation: pulse 0.8s infinite;
}

/* --- Modal --- */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.6);
    display: flex;
    justify-content: center;
    align-items: center;
    backdrop-filter: blur(8px);
    z-index: 1000;
    opacity: 0;
    transition: opacity 0.4s ease;
    animation: fadeIn 0.4s forwards;
}

.modal-content {
    background: var(--board-bg);
    padding: 3rem 4rem;
    border-radius: 25px;
    border: 1px solid rgba(255, 255, 255, 0.2);
    text-align: center;
    box-shadow: 0 8px 40px var(--shadow-color);
    animation: popIn 0.5s ease-out forwards;
}

.modal-content p {
    font-size: 2.2rem;
    font-weight: 600;
    margin-bottom: 2rem;
    text-shadow: 0 0 5px var(--glow-color);
}

.modal-buttons button {
    padding: 1rem 2rem;
    font-size: 1.1rem;
    font-weight: 600;
    margin: 0 0.5rem;
    border: 1px solid rgba(255, 255, 255, 0.3);
    border-radius: 50px;
    cursor: pointer;
    background: var(--cell-bg);
    color: var(--text-color);
}

.modal-buttons button:hover {
    transform: translateY(-3px);
    background: rgba(255, 255, 255, 0.2);
    box-shadow: 0 0 10px var(--glow-color);
}

/* --- Utility & Animations --- */
.hidden {
    display: none !important;
    opacity: 0;
    transform: scale(0.9);
}

@keyframes fadeInDown { from { opacity: 0; transform: translateY(-30px); } to { opacity: 1; transform: translateY(0); } }
@keyframes fadeInUp { from { opacity: 0; transform: translateY(30px); } to { opacity: 1; transform: translateY(0); } }
@keyframes zoomIn { from { opacity: 0; transform: scale(0.8); } to { opacity: 1; transform: scale(1); } }
@keyframes fadeIn { from { opacity: 0; } to { opacity: 1; } }
@keyframes popIn {
    from { transform: scale(0.5); opacity: 0; }
    to { transform: scale(1); opacity: 1; }
}
@keyframes pulse {
    0%, 100% { transform: scale(1); box-shadow: none; }
    50% { transform: scale(1.05); box-shadow: 0 0 20px var(--glow-color); }
}

/* --- Responsive Design --- */
@media (max-width: 600px) {
    .title { font-size: 3.5rem; }
    .scoreboard-card { flex-direction: column; gap: 0.8rem; padding: 1rem; }
    .score-item { font-size: 1.1rem; }
    .turn-indicator { font-size: 1.3rem; }
    .modal-content { padding: 2rem; width: 90%; }
    .modal-content p { font-size: 1.8rem; }
    .modal-buttons { display: flex; flex-direction: column; gap: 1rem; }
}