:root {
    --bg-color: #f4f4f9;
    --text-color: #333;
    --border-color: #ccc;
    --element-bg: #fff;

    /* Category Colors */
    --nonmetal: #a0e6ff;
    --noble-gas: #ffc0cb;
    --alkali-metal: #ff9999;
    --alkaline-earth: #ffdead;
    --metalloid: #cccc99;
    --halogen: #ffff99;
    --metal: #c0c0c0;
    --transition-metal: #ffc0a0;
    --lanthanide: #ffb6c1;
    --actinide: #f08080;
    --unknown: #e0e0e0;
}

/* ── Layout ── */

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    padding: 0;
}

#app {
    display: flex;
    flex-direction: column;
    align-items: center;
    width: 100%;
    height: 100dvh;
    padding: 8px;
    box-sizing: border-box;
    overflow: hidden;
}

header {
    margin-bottom: 4px;
    flex-shrink: 0;
}

header h1 {
    margin: 4px 0;
    font-size: 1.3rem;
}

main {
    width: 100%;
    max-width: 900px;
    flex: 1;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 0;
}

/* ── Main Grid ── */

.periodic-table {
    display: grid;
    grid-template-columns: 22px repeat(7, minmax(0, 1fr)) repeat(3, minmax(0, 1fr));
    grid-template-rows: 20px repeat(11, minmax(0, 1fr));
    gap: 2px;
    width: 100%;
    aspect-ratio: 14 / 10;
}

/* ── f-block (Lanthanides / Actinides) ── */

.f-block {
    display: grid;
    grid-template-columns: repeat(14, minmax(0, 1fr));
    grid-template-rows: repeat(2, minmax(0, 1fr));
    gap: 2px;
    margin-top: 6px;
    width: 100%;
    aspect-ratio: 14 / 1.8;
}

/* ── Grid Headers ── */

.grid-header {
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
    font-size: 0.75rem;
    color: #666;
}

.period-header {
    writing-mode: vertical-rl;
    text-orientation: mixed;
    transform: rotate(180deg);
}

/* ── Element Cell ── */

.element {
    border: 1px solid var(--border-color);
    box-sizing: border-box;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    cursor: pointer;
    background-color: var(--element-bg);
    transition: transform 0.1s, box-shadow 0.1s;
    font-size: 0.7rem;
    padding: 1px 2px;
    overflow: hidden;
}

.top-row {
    display: flex;
    justify-content: space-between;
    width: 100%;
    align-items: baseline;
    line-height: 1;
}

.subgroup-a  { align-items: flex-start; }
.subgroup-b  { align-items: flex-end; }
.subgroup-viii { align-items: center; }

.element:hover {
    transform: scale(1.15);
    box-shadow: 0 4px 8px rgba(0,0,0,0.2);
    z-index: 10;
}

.element .number { font-size: 0.65rem; }
.element .mass   { font-size: 0.6rem; color: #444; }

.element .symbol {
    font-weight: bold;
    font-size: 1.1rem;
    line-height: 1.1;
}

.element .name {
    font-size: 0.55rem;
    text-align: center;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    width: 100%;
    align-self: center;
    line-height: 1.1;
}

/* ── Modal ── */

.modal {
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background-color: rgba(0,0,0,0.5);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.modal.hidden { display: none !important; }

.modal-content {
    background-color: #fff;
    padding: 20px 30px;
    border-radius: 8px;
    width: 90%;
    max-width: 600px;
    max-height: 90vh;
    overflow-y: auto;
    position: relative;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}

.close {
    position: absolute;
    top: 12px; right: 16px;
    font-size: 1.5rem;
    font-weight: bold;
    cursor: pointer;
    color: #888;
}
.close:hover { color: #333; }

.modal-header {
    text-align: center;
    margin-bottom: 16px;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 8px;
}

.modal-body {
    display: flex;
    justify-content: center;
    align-items: flex-start;
    flex-wrap: wrap;
    gap: 20px;
}

.bohr-model-container {
    flex: 1 1 280px;
    display: flex;
    justify-content: center;
}

.electron-configuration {
    flex: 0 0 180px;
    background: #f9f9f9;
    padding: 12px;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

#electron-list {
    list-style-type: none;
    padding: 0; margin: 0;
}

#electron-list li {
    padding: 4px 0;
    border-bottom: 1px solid #ddd;
    display: flex;
    justify-content: space-between;
}
#electron-list li:last-child { border-bottom: none; }

/* ── Bohr model animation ── */

@keyframes rotateShell {
    from { transform: rotate(0deg); }
    to   { transform: rotate(360deg); }
}

.electron-shell {
    transform-origin: 200px 200px;
}

/* ── Tablet / small screens ── */

@media (max-height: 700px), (max-width: 820px) {
    #app {
        height: auto;
        min-height: 100dvh;
        overflow: auto;
    }

    .periodic-table {
        grid-template-rows: 18px repeat(11, 32px);
        flex: none;
    }

    .f-block {
        grid-template-rows: repeat(2, 32px);
        flex: none;
    }

    .element .symbol { font-size: 0.8rem; }
    .element .number { font-size: 0.5rem; }
    .element .mass   { font-size: 0.45rem; }
    .element .name   { font-size: 0.4rem; }
}