:root {
    /* Cosmic pastel neon colors */
    --color-alkali-metal: #FF69B4; /* Hot Pink */
    --color-alkaline-earth-metal: #BA55D3; /* Medium Orchid */
    --color-transition-metal: #ADFF2F; /* Green Yellow */
    --color-post-transition-metal: #00FFFF; /* Aqua */
    --color-metalloid: #FFD700; /* Gold */
    --color-nonmetal: #7B68EE; /* Medium Slate Blue */
    --color-halogen: #FF4500; /* Orange Red */
    --color-noble-gas: #8A2BE2; /* Blue Violet */
    --color-lanthanide: #EE82EE; /* Violet */
    --color-actinide: #98FB98; /* Pale Green */
    --color-unknown: #808080; /* Grey */

    --bg-color-dark: #1a0f30; /* Dark purple/blue for cosmic feel */
    --text-color-light: #e0e0e0;
    --card-bg: rgba(40, 20, 80, 0.7); /* Slightly lighter, transparent card background */
    --border-color: rgba(255, 255, 255, 0.2);
    --hover-glow: 0 0 15px rgba(255, 255, 255, 0.6);
}

body {
    font-family: 'JetBrains Mono', monospace;
    background: radial-gradient(circle at top left, var(--bg-color-dark) 0%, #0a0515 100%);
    color: var(--text-color-light);
    margin: 0;
    padding: 20px;
    display: flex;
    flex-direction: column; /* Arrange items in a column */
    justify-content: space-between; /* Push content to top, footer to bottom */
    min-height: 100vh; /* Ensure body takes at least full viewport height */
    box-sizing: border-box;
}

.container {
    max-width: 1400px;
    width: 100%;
    margin: 0 auto; /* Center the container horizontally */
    background-color: rgba(0, 0, 0, 0.3); /* Slightly transparent overlay for content */
    border-radius: 15px;
    padding: 30px;
    box-shadow: 0 0 30px rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(5px); /* Frosted glass effect */
    flex-grow: 1; /* Allow container to grow and push footer down */
}

h1.pixel-font {
    font-family: 'Press Start 2P', cursive; /* Minecraft pixel font */
    text-align: center;
    color: var(--text-color-light);
    margin-bottom: 10px; /* Reduced margin to fit tagline */
    text-shadow: 0 0 10px rgba(255, 255, 255, 0.3);
    font-size: 2.5em; /* Adjust size for pixel font */
}

.tagline {
    font-family: 'Quicksand', sans-serif;
    text-align: center;
    font-size: 1.1em;
    color: rgba(255, 255, 255, 0.7);
    margin-bottom: 30px;
}

.filters {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    justify-content: center;
    margin-bottom: 20px; /* Reduced margin to fit color index */
}

.filter-group label {
    margin-right: 10px;
    font-weight: bold;
    color: var(--text-color-light);
}

.filter-group select {
    padding: 8px 12px;
    border-radius: 8px;
    border: 1px solid var(--border-color);
    background-color: var(--card-bg);
    color: var(--text-color-light);
    font-family: 'JetBrains Mono', monospace;
    appearance: none; /* Remove default arrow */
    -webkit-appearance: none;
    -moz-appearance: none;
    background-image: url('data:image/svg+xml;charset=US-ASCII,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20width%3D%22292.4%22%20height%3D%22292.4%22%3E%3Cpath%20fill%3D%22%23e0e0e0%22%20d%3D%22M287%2C197.971L146.205%2C57.176L5.41%2C197.971L0%2C192.561L146.205%2C46.356L292.41%2C192.561L287%2C197.971z%22%2F%3E%3C%2Fsvg%3E');
    background-repeat: no-repeat;
    background-position: right 10px top 50%;
    background-size: 12px auto;
    cursor: pointer;
    transition: all 0.3s ease;
}

.filter-group select:hover {
    border-color: rgba(255, 255, 255, 0.4);
    box-shadow: var(--hover-glow);
}

/* Color Index Styling */
.color-index {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 15px; /* Space between each color item */
    margin-bottom: 30px;
    padding: 10px;
    background-color: rgba(255, 255, 255, 0.03);
    border-radius: 10px;
    font-size: 0.9em; /* Same size as other texts */
}

.color-index-item {
    display: flex;
    align-items: center;
    gap: 5px;
}

.color-swatch {
    width: 18px;
    height: 18px;
    border-radius: 4px;
    border: 1px solid rgba(255, 255, 255, 0.2);
}

/* Color swatch backgrounds - dynamically set by JS, but defined here for consistency */
.swatch-alkali-metal { background-color: var(--color-alkali-metal); }
.swatch-alkaline-earth-metal { background-color: var(--color-alkaline-earth-metal); }
.swatch-transition-metal { background-color: var(--color-transition-metal); }
.swatch-post-transition-metal { background-color: var(--color-post-transition-metal); }
.swatch-metalloid { background-color: var(--color-metalloid); }
.swatch-nonmetal { background-color: var(--color-nonmetal); }
.swatch-halogen { background-color: var(--color-halogen); }
.swatch-noble-gas { background-color: var(--color-noble-gas); }
.swatch-lanthanide { background-color: var(--color-lanthanide); }
.swatch-actinide { background-color: var(--color-actinide); }
.swatch-unknown { background-color: var(--color-unknown); }


#periodic-table-grid {
    display: grid;
    grid-template-columns: repeat(18, 1fr);
    gap: 5px;
    background-color: rgba(255, 255, 255, 0.05); /* Subtle grid background */
    padding: 10px;
    border-radius: 10px;
    overflow-x: auto;
    min-height: 700px; /* Keep this for consistent height */
    position: relative;
}

/* Base element card styling */
.element-card {
    background-color: var(--card-bg);
    border-radius: 10px;
    padding: 10px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    cursor: pointer;
    transition: transform 0.2s ease-in-out, box-shadow 0.2s ease-in-out;
    border: 1px solid var(--border-color);
    box-shadow: 0 0 5px rgba(0, 0, 0, 0.3);
    position: relative;
    overflow: hidden;
    aspect-ratio: 1 / 1.2; /* Maintain a consistent aspect ratio */
}

.element-card:hover {
    transform: translateY(-5px) scale(1.05);
    box-shadow: var(--hover-glow);
    z-index: 10;
}

.element-card.hidden {
    display: none; /* This ensures hidden elements don't take up grid space */
}

.element-card .atomic-number {
    font-size: 0.7em;
    position: absolute;
    top: 5px;
    left: 5px;
    color: rgba(255, 255, 255, 0.7);
}

.element-card .symbol {
    font-size: 1.8em;
    font-weight: bold;
    margin-top: 5px;
    margin-bottom: 5px;
    line-height: 1;
}

.element-card .name {
    font-size: 0.6em;
    word-wrap: break-word;
    white-space: normal;
    overflow: hidden;
    text-overflow: ellipsis;
    max-height: 2.4em; /* Approx 2 lines */
}

/* Category-based coloring */
.category-alkali-metal { background-color: var(--color-alkali-metal); }
.category-alkaline-earth-metal { background-color: var(--color-alkaline-earth-metal); }
.category-transition-metal { background-color: var(--color-transition-metal); }
.category-post-transition-metal { background-color: var(--color-post-transition-metal); }
.category-metalloid { background-color: var(--color-metalloid); }
.category-nonmetal { background-color: var(--color-nonmetal); }
.category-halogen { background-color: var(--color-halogen); }
.category-noble-gas { background-color: var(--color-noble-gas); }
.category-lanthanide { background-color: var(--color-lanthanide); }
.category-actinide { background-color: var(--color-actinide); }
.category-unknown { background-color: var(--color-unknown); } /* For elements with unknown categories initially */


/* Positioning for the main periodic table elements */
/* These are fixed positions based on the standard periodic table layout */
.element-card[data-atomic-number="1"] { grid-column: 1; grid-row: 1; }
.element-card[data-atomic-number="2"] { grid-column: 18; grid-row: 1; }
.element-card[data-atomic-number="3"] { grid-column: 1; grid-row: 2; }
.element-card[data-atomic-number="4"] { grid-column: 2; grid-row: 2; }
.element-card[data-atomic-number="5"] { grid-column: 13; grid-row: 2; }
.element-card[data-atomic-number="6"] { grid-column: 14; grid-row: 2; }
.element-card[data-atomic-number="7"] { grid-column: 15; grid-row: 2; }
.element-card[data-atomic-number="8"] { grid-column: 16; grid-row: 2; }
.element-card[data-atomic-number="9"] { grid-column: 17; grid-row: 2; }
.element-card[data-atomic-number="10"] { grid-column: 18; grid-row: 2; }
.element-card[data-atomic-number="11"] { grid-column: 1; grid-row: 3; }
.element-card[data-atomic-number="12"] { grid-column: 2; grid-row: 3; }
.element-card[data-atomic-number="13"] { grid-column: 13; grid-row: 3; }
.element-card[data-atomic-number="14"] { grid-column: 14; grid-row: 3; }
.element-card[data-atomic-number="15"] { grid-column: 15; grid-row: 3; }
.element-card[data-atomic-number="16"] { grid-column: 16; grid-row: 3; }
.element-card[data-atomic-number="17"] { grid-column: 17; grid-row: 3; }
.element-card[data-atomic-number="18"] { grid-column: 18; grid-row: 3; }
.element-card[data-atomic-number="19"] { grid-column: 1; grid-row: 4; }
.element-card[data-atomic-number="20"] { grid-column: 2; grid-row: 4; }
.element-card[data-atomic-number="21"] { grid-column: 3; grid-row: 4; }
.element-card[data-atomic-number="22"] { grid-column: 4; grid-row: 4; }
.element-card[data-atomic-number="23"] { grid-column: 5; grid-row: 4; }
.element-card[data-atomic-number="24"] { grid-column: 6; grid-row: 4; }
.element-card[data-atomic-number="25"] { grid-column: 7; grid-row: 4; }
.element-card[data-atomic-number="26"] { grid-column: 8; grid-row: 4; }
.element-card[data-atomic-number="27"] { grid-column: 9; grid-row: 4; }
.element-card[data-atomic-number="28"] { grid-column: 10; grid-row: 4; }
.element-card[data-atomic-number="29"] { grid-column: 11; grid-row: 4; }
.element-card[data-atomic-number="30"] { grid-column: 12; grid-row: 4; }
.element-card[data-atomic-number="31"] { grid-column: 13; grid-row: 4; }
.element-card[data-atomic-number="32"] { grid-column: 14; grid-row: 4; }
.element-card[data-atomic-number="33"] { grid-column: 15; grid-row: 4; }
.element-card[data-atomic-number="34"] { grid-column: 16; grid-row: 4; }
.element-card[data-atomic-number="35"] { grid-column: 17; grid-row: 4; }
.element-card[data-atomic-number="36"] { grid-column: 18; grid-row: 4; }
.element-card[data-atomic-number="37"] { grid-column: 1; grid-row: 5; }
.element-card[data-atomic-number="38"] { grid-column: 2; grid-row: 5; }
.element-card[data-atomic-number="39"] { grid-column: 3; grid-row: 5; }
.element-card[data-atomic-number="40"] { grid-column: 4; grid-row: 5; }
.element-card[data-atomic-number="41"] { grid-column: 5; grid-row: 5; }
.element-card[data-atomic-number="42"] { grid-column: 6; grid-row: 5; }
.element-card[data-atomic-number="43"] { grid-column: 7; grid-row: 5; }
.element-card[data-atomic-number="44"] { grid-column: 8; grid-row: 5; }
.element-card[data-atomic-number="45"] { grid-column: 9; grid-row: 5; }
.element-card[data-atomic-number="46"] { grid-column: 10; grid-row: 5; }
.element-card[data-atomic-number="47"] { grid-column: 11; grid-row: 5; }
.element-card[data-atomic-number="48"] { grid-column: 12; grid-row: 5; }
.element-card[data-atomic-number="49"] { grid-column: 13; grid-row: 5; }
.element-card[data-atomic-number="50"] { grid-column: 14; grid-row: 5; }
.element-card[data-atomic-number="51"] { grid-column: 15; grid-row: 5; }
.element-card[data-atomic-number="52"] { grid-column: 16; grid-row: 5; }
.element-card[data-atomic-number="53"] { grid-column: 17; grid-row: 5; }
.element-card[data-atomic-number="54"] { grid-column: 18; grid-row: 5; }
.element-card[data-atomic-number="55"] { grid-column: 1; grid-row: 6; }
.element-card[data-atomic-number="56"] { grid-column: 2; grid-row: 6; }
/* Lanthanide label placeholder */
.element-card[data-atomic-number="72"] { grid-column: 4; grid-row: 6; }
.element-card[data-atomic-number="73"] { grid-column: 5; grid-row: 6; }
.element-card[data-atomic-number="74"] { grid-column: 6; grid-row: 6; }
.element-card[data-atomic-number="75"] { grid-column: 7; grid-row: 6; }
.element-card[data-atomic-number="76"] { grid-column: 8; grid-row: 6; }
.element-card[data-atomic-number="77"] { grid-column: 9; grid-row: 6; }
.element-card[data-atomic-number="78"] { grid-column: 10; grid-row: 6; }
.element-card[data-atomic-number="79"] { grid-column: 11; grid-row: 6; }
.element-card[data-atomic-number="80"] { grid-column: 12; grid-row: 6; }
.element-card[data-atomic-number="81"] { grid-column: 13; grid-row: 6; }
.element-card[data-atomic-number="82"] { grid-column: 14; grid-row: 6; }
.element-card[data-atomic-number="83"] { grid-column: 15; grid-row: 6; }
.element-card[data-atomic-number="84"] { grid-column: 16; grid-row: 6; }
.element-card[data-atomic-number="85"] { grid-column: 17; grid-row: 6; }
.element-card[data-atomic-number="86"] { grid-column: 18; grid-row: 6; }
.element-card[data-atomic-number="87"] { grid-column: 1; grid-row: 7; }
.element-card[data-atomic-number="88"] { grid-column: 2; grid-row: 7; }
/* Actinide label placeholder */
.element-card[data-atomic-number="104"] { grid-column: 4; grid-row: 7; }
.element-card[data-atomic-number="105"] { grid-column: 5; grid-row: 7; }
.element-card[data-atomic-number="106"] { grid-column: 6; grid-row: 7; }
.element-card[data-atomic-number="107"] { grid-column: 7; grid-row: 7; }
.element-card[data-atomic-number="108"] { grid-column: 8; grid-row: 7; }
.element-card[data-atomic-number="109"] { grid-column: 9; grid-row: 7; }
.element-card[data-atomic-number="110"] { grid-column: 10; grid-row: 7; }
.element-card[data-atomic-number="111"] { grid-column: 11; grid-row: 7; }
.element-card[data-atomic-number="112"] { grid-column: 12; grid-row: 7; }
.element-card[data-atomic-number="113"] { grid-column: 13; grid-row: 7; }
.element-card[data-atomic-number="114"] { grid-column: 14; grid-row: 7; }
.element-card[data-atomic-number="115"] { grid-column: 15; grid-row: 7; }
.element-card[data-atomic-number="116"] { grid-column: 16; grid-row: 7; }
.element-card[data-atomic-number="117"] { grid-column: 17; grid-row: 7; }
.element-card[data-atomic-number="118"] { grid-column: 18; grid-row: 7; }


/* Styles for Lanthanide/Actinide text labels - these indicate the series location */
.lanthanide-label,
.actinide-label {
    /* Position them in the main grid where the La/Ac placeholder would be */
    grid-column: 3 / span 10; /* Span columns where f-block would be */
    padding: 5px; /* Adjust padding as needed */
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 0.8em; /* Slightly larger for visibility */
    font-weight: bold;
    color: rgba(255, 255, 255, 0.6); /* Softer text color */
    background-color: rgba(40, 20, 80, 0.3); /* Subtle background */
    border-radius: 8px;
    text-align: center;
    pointer-events: none; /* Make sure it's not clickable */
    user-select: none; /* Prevent text selection */
}

.lanthanide-label {
    grid-row: 6; /* Position in the 6th row of the main grid */
}

.actinide-label {
    grid-row: 7; /* Position in the 7th row of the main grid */
}

/* Lanthanides and Actinides block - placed below the main table */
.lanthanides-actinides {
    grid-column: 1 / -1; /* Span all columns */
    display: grid;
    grid-template-columns: repeat(14, 1fr); /* 14 columns for f-block */
    gap: 5px;
    margin-top: 40px; /* Space between main table and f-block */
    padding: 10px;
    background-color: rgba(255, 255, 255, 0.05);
    border-radius: 10px;
}

/* Specific positioning within the lanthanides/actinides block (14 elements per row) */
.lanthanides-actinides .element-card[data-atomic-number="57"] { grid-column: 1; }
.lanthanides-actinides .element-card[data-atomic-number="58"] { grid-column: 2; }
.lanthanides-actinides .element-card[data-atomic-number="59"] { grid-column: 3; }
.lanthanides-actinides .element-card[data-atomic-number="60"] { grid-column: 4; }
.lanthanides-actinides .element-card[data-atomic-number="61"] { grid-column: 5; }
.lanthanides-actinides .element-card[data-atomic-number="62"] { grid-column: 6; }
.lanthanides-actinides .element-card[data-atomic-number="63"] { grid-column: 7; }
.lanthanides-actinides .element-card[data-atomic-number="64"] { grid-column: 8; }
.lanthanides-actinides .element-card[data-atomic-number="65"] { grid-column: 9; }
.lanthanides-actinides .element-card[data-atomic-number="66"] { grid-column: 10; }
.lanthanides-actinides .element-card[data-atomic-number="67"] { grid-column: 11; }
.lanthanides-actinides .element-card[data-atomic-number="68"] { grid-column: 12; }
.lanthanides-actinides .element-card[data-atomic-number="69"] { grid-column: 13; }
.lanthanides-actinides .element-card[data-atomic-number="70"] { grid-column: 14; }
.lanthanides-actinides .element-card[data-atomic-number="71"] { grid-column: 15; } /* Lu is technically d-block, but often grouped here */

.lanthanides-actinides .element-card[data-atomic-number="89"] { grid-column: 1; }
.lanthanides-actinides .element-card[data-atomic-number="90"] { grid-column: 2; }
.lanthanides-actinides .element-card[data-atomic-number="91"] { grid-column: 3; }
.lanthanides-actinides .element-card[data-atomic-number="92"] { grid-column: 4; }
.lanthanides-actinides .element-card[data-atomic-number="93"] { grid-column: 5; }
.lanthanides-actinides .element-card[data-atomic-number="94"] { grid-column: 6; }
.lanthanides-actinides .element-card[data-atomic-number="95"] { grid-column: 7; }
.lanthanides-actinides .element-card[data-atomic-number="96"] { grid-column: 8; }
.lanthanides-actinides .element-card[data-atomic-number="97"] { grid-column: 9; }
.lanthanides-actinides .element-card[data-atomic-number="98"] { grid-column: 10; }
.lanthanides-actinides .element-card[data-atomic-number="99"] { grid-column: 11; }
.lanthanides-actinides .element-card[data-atomic-number="100"] { grid-column: 12; }
.lanthanides-actinides .element-card[data-atomic-number="101"] { grid-column: 13; }
.lanthanides-actinides .element-card[data-atomic-number="102"] { grid-column: 14; }
.lanthanides-actinides .element-card[data-atomic-number="103"] { grid-column: 15; } /* Lr is technically d-block, but often grouped here */


/* Modal Styling */
.modal {
    display: none; /* Hidden by default - IMPORTANT for stopping it on load */
    position: fixed; /* Stay in place */
    z-index: 100; /* Sit on top */
    left: 0;
    top: 0;
    width: 100%; /* Full width */
    height: 100%; /* Full height */
    overflow: auto; /* Enable scroll if needed */
    background-color: rgba(0, 0, 0, 0.6); /* Black w/ opacity */
    backdrop-filter: blur(5px);
    /* The next two lines will be active when JS sets display:flex */
    justify-content: center;
    align-items: center;
}

.modal-content {
    background-color: var(--card-bg);
    margin: auto;
    padding: 30px;
    border: 1px solid var(--border-color);
    border-radius: 15px;
    width: 80%;
    max-width: 500px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.5);
    position: relative;
    color: var(--text-color-light);
    animation: fadeIn 0.3s ease-out;
}

@keyframes fadeIn {
    from { opacity: 0; transform: scale(0.9); }
    to { opacity: 1; transform: scale(1); }
}

.modal-content h2 {
    font-family: 'Quicksand', sans-serif;
    color: var(--text-color-light);
    text-align: center;
    margin-top: 0;
    margin-bottom: 20px;
    text-shadow: 0 0 8px rgba(255, 255, 255, 0.2);
}

.modal-content p {
    margin-bottom: 10px;
    line-height: 1.6;
}

.modal-content strong {
    color: rgba(255, 255, 255, 0.8);
}

.close-button {
    color: var(--text-color-light);
    position: absolute;
    top: 15px;
    right: 25px;
    font-size: 30px;
    font-weight: bold;
    cursor: pointer;
    transition: color 0.3s ease;
}

.close-button:hover,
.close-button:focus {
    color: var(--color-halogen); /* A contrasting color for hover */
    text-decoration: none;
}

footer {
    margin-top: 40px;
    padding: 20px;
    color: rgba(255, 255, 255, 0.5);
    font-size: 0.9em;
    text-align: center;
    width: 100%; /* Ensure footer spans full width */
    box-sizing: border-box;
}

/* Responsive adjustments */
@media (max-width: 1200px) {
    #periodic-table-grid {
        grid-template-columns: repeat(18, minmax(60px, 1fr)); /* Allow smaller cards */
    }
    h1.pixel-font {
        font-size: 2em;
    }
    .color-index {
        font-size: 0.8em;
        gap: 10px;
    }
    .color-swatch {
        width: 15px;
        height: 15px;
    }
}

@media (max-width: 992px) {
    #periodic-table-grid {
        grid-template-columns: repeat(18, minmax(50px, 1fr));
        gap: 3px;
        font-size: 0.9em;
    }
    .element-card .symbol {
        font-size: 1.5em;
    }
    .element-card .name {
        font-size: 0.55em;
    }
    .container {
        padding: 20px;
    }
    h1.pixel-font {
        font-size: 1.8em;
    }
    .tagline {
        font-size: 1em;
    }
    .color-index {
        font-size: 0.75em;
        gap: 8px;
        padding: 8px;
    }
    .color-swatch {
        width: 14px;
        height: 14px;
    }
}

@media (max-width: 768px) {
    body {
        padding: 10px;
    }
    .container {
        padding: 15px;
    }
    h1.pixel-font {
        font-size: 1.5em;
    }
    .tagline {
        font-size: 0.9em;
    }
    .filters {
        flex-direction: column;
        align-items: center;
    }
    #periodic-table-grid {
        grid-template-columns: repeat(18, minmax(40px, 1fr));
        gap: 2px;
        font-size: 0.8em;
    }
    .element-card {
        padding: 5px;
    }
    .element-card .symbol {
        font-size: 1.2em;
    }
    .element-card .name {
        font-size: 0.5em;
    }
    .modal-content {
        width: 90%;
        padding: 20px;
    }
    .close-button {
        font-size: 24px;
        top: 10px;
        right: 20px;
    }
    .lanthanide-label,
    .actinide-label {
        font-size: 0.6em; /* Even smaller for consistency */
        padding: 2px;
    }
    .color-index {
        font-size: 0.7em;
        gap: 6px;
        padding: 6px;
    }
    .color-swatch {
        width: 12px;
        height: 12px;
    }
}

@media (max-width: 480px) {
    h1.pixel-font {
        font-size: 1.2em; /* Smaller for very small screens */
    }
    .tagline {
        font-size: 0.8em;
    }
    .filter-group select {
        width: 100%;
    }
    #periodic-table-grid {
        grid-template-columns: repeat(18, minmax(35px, 1fr));
        gap: 1px;
    }
    .element-card .atomic-number {
        font-size: 0.6em;
        top: 2px;
        left: 2px;
    }
    .element-card .symbol {
        font-size: 1em;
    }
    .element-card .name {
        font-size: 0.45em;
    }
    footer {
        font-size: 0.7em;
    }
    .color-index {
        font-size: 0.6em;
        gap: 4px;
        padding: 4px;
    }
    .color-swatch {
        width: 10px;
        height: 10px;
    }
}