@import url('https://fonts.googleapis.com/css2?family=Orbitron:wght@700;900&family=Share+Tech+Mono&display=swap');

:root {
    --bg:        #0b0f0e;
    --surface:   #111816;
    --surface2:  #162018;
    --border:    #39ff6a44;
    --glow:      #39ff6a;
    --glow-soft: #39ff6a22;
    --text:      #c8ffd4;
    --text-dim:  #4d8a5a;
    --error:     #ff4444;
    --warn:      #ffb500;
}

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

body {
    background-color: var(--bg);
    background-image:
        radial-gradient(ellipse at 50% 0%, #0d2d1a 0%, transparent 65%),
        repeating-linear-gradient(0deg, transparent, transparent 3px, #ffffff05 3px, #ffffff05 4px);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 2rem 1rem;
    font-family: 'Share Tech Mono', monospace;
    color: var(--text);
}

/* ── Header ─────────────────────────────────── */
header {
    text-align: center;
    margin-bottom: 1.5rem;
}

header h1 {
    font-family: 'Orbitron', sans-serif;
    font-weight: 900;
    font-size: clamp(1.6rem, 5vw, 2.8rem);
    letter-spacing: 0.2em;
    color: var(--glow);
    text-shadow: 0 0 8px var(--glow), 0 0 24px var(--glow);
    animation: flicker 9s infinite;
}

header p {
    font-size: 0.72rem;
    letter-spacing: 0.18em;
    color: var(--text-dim);
    margin-top: 0.3rem;
    text-transform: uppercase;
}

@keyframes flicker {
    0%,94%,96%,98%,100% { opacity: 1; }
    95%,97%              { opacity: .6; }
}

/* ── HUD (controls bar) ─────────────────────── */
.hud {
    width: 100%;
    max-width: 430px;
    display: flex;
    align-items: center;
    gap: 0.6rem;
    flex-wrap: wrap;
    margin-bottom: 1rem;
}

.hud select {
    background: var(--surface);
    border: 1px solid var(--border);
    color: var(--text);
    font-family: 'Share Tech Mono', monospace;
    font-size: 0.72rem;
    letter-spacing: 0.08em;
    padding: 0.35rem 0.6rem;
    cursor: pointer;
    outline: none;
    transition: border-color .15s, box-shadow .15s;
    flex: 1;
    min-width: 110px;
}

.hud select:hover,
.hud select:focus {
    border-color: var(--glow);
    box-shadow: 0 0 8px var(--glow);
}

.btn {
    background: transparent;
    border: 1px solid var(--border);
    color: var(--text);
    font-family: 'Share Tech Mono', monospace;
    font-size: 0.68rem;
    letter-spacing: 0.1em;
    padding: 0.35rem 0.8rem;
    cursor: pointer;
    text-transform: uppercase;
    transition: border-color .15s, box-shadow .15s, background .15s;
    white-space: nowrap;
}

.btn:hover {
    border-color: var(--glow);
    box-shadow: 0 0 10px var(--glow);
    background: var(--glow-soft);
    color: var(--glow);
}

/* ── Stats bar ──────────────────────────────── */
.stats {
    width: 100%;
    max-width: 430px;
    display: flex;
    justify-content: space-between;
    font-size: 0.72rem;
    letter-spacing: 0.1em;
    color: var(--text-dim);
    margin-bottom: 0.8rem;
}

.stats span { color: var(--glow); }

/* ── Board wrapper (glow frame) ─────────────── */
.board-wrap {
    position: relative;
    padding: 3px;
    background: linear-gradient(135deg, var(--glow) 0%, transparent 60%);
    box-shadow: 0 0 20px var(--glow), 0 0 60px #39ff6a33;
}

.board-wrap::before,
.board-wrap::after,
.board-wrap > .corner-bl,
.board-wrap > .corner-br {
    content: '';
    position: absolute;
    width: 10px;
    height: 10px;
    border-color: var(--glow);
    border-style: solid;
    z-index: 1;
}
.board-wrap::before  { top: -2px;    left: -2px;    border-width: 2px 0 0 2px; }
.board-wrap::after   { top: -2px;    right: -2px;   border-width: 2px 2px 0 0; }
.board-wrap > .corner-bl { bottom: -2px; left: -2px;  border-width: 0 0 2px 2px; }
.board-wrap > .corner-br { bottom: -2px; right: -2px; border-width: 0 2px 2px 0; }

/* ── Sudoku Board ───────────────────────────── */
#sudokuBoard {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 0;
    width: 360px;
    height: 360px;
    background: var(--surface);
}

.sudoku-cell {
    background: var(--surface);
    border: 1px solid #1e3a28;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
}

/* thick borders for 3×3 boxes */
.sudoku-cell:nth-child(3n)               { border-right:  2px solid #39ff6a66; }
.sudoku-cell:nth-child(9n+1)             { border-left:   2px solid #39ff6a66; }
.sudoku-cell:nth-child(n+1):nth-child(-n+9)   { border-top:    2px solid #39ff6a66; }
.sudoku-cell:nth-child(n+28):nth-child(-n+36) { border-top:    2px solid #39ff6a66; }
.sudoku-cell:nth-child(n+55):nth-child(-n+63) { border-top:    2px solid #39ff6a66; }
.sudoku-cell:nth-child(n+73):nth-child(-n+81) { border-bottom: 2px solid #39ff6a66; }

.sudoku-cell input {
    width: 100%;
    height: 100%;
    border: none;
    background: transparent;
    color: #7dffaa;
    font-family: 'Share Tech Mono', monospace;
    font-size: 1rem;
    text-align: center;
    padding: 0;
    cursor: pointer;
    caret-color: var(--glow);
}

.sudoku-cell input:focus {
    outline: none;
    background: #39ff6a18;
    color: var(--glow);
    text-shadow: 0 0 6px var(--glow);
}

.sudoku-cell.given {
    background: var(--surface2);
}

.sudoku-cell.given input {
    color: var(--text);
    font-weight: bold;
    cursor: default;
}

.sudoku-cell.highlight {
    background: #39ff6a0d;
}

.sudoku-cell.error {
    background: #ff444422;
}

.sudoku-cell.error input {
    color: var(--error);
    text-shadow: 0 0 6px var(--error);
}

/* ── Status message ─────────────────────────── */
#statusMessage {
    width: 100%;
    max-width: 430px;
    margin-top: 0.8rem;
    padding: 0.5rem 1rem;
    font-size: 0.75rem;
    letter-spacing: 0.1em;
    border: 1px solid var(--border);
    background: var(--surface);
    color: var(--glow);
    text-align: center;
    display: none;
    animation: fadeIn .3s ease-in;
}

#statusMessage.danger {
    border-color: var(--error);
    color: var(--error);
    box-shadow: 0 0 8px var(--error);
}

#statusMessage.success {
    border-color: var(--glow);
    color: var(--glow);
    box-shadow: 0 0 8px var(--glow);
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-4px); }
    to   { opacity: 1; transform: translateY(0); }
}

/* ── Responsive ─────────────────────────────── */
@media (max-width: 500px) {
    #sudokuBoard { width: 288px; height: 288px; }
    .sudoku-cell input { font-size: 0.85rem; }
    .hud { max-width: 288px; }
    .stats { max-width: 288px; }
}