/* ══════════════════════════ RESET & ROOT ══════════════════════════ */
:root {
    --bg: #060810;
    --surface: #0d1424;
    --surface2: #182035;
    --primary: #6366f1;
    --primary-glow: rgba(99,102,241,0.25);
    --gold: #facc15;
    --gold-glow: rgba(250,204,21,0.2);
    --green: #34d399;
    --pink: #f472b6;
    --text: #f1f5f9;
    --muted: #64748b;
    --border: rgba(255,255,255,0.06);
    --card-bg: rgba(255,255,255,0.03);
}

*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
body{font-family:'Outfit',sans-serif;background:var(--bg);color:var(--text);height:100vh;overflow:hidden}

/* ══════════════════════════ BG CANVAS ══════════════════════════ */
#bgCanvas{position:fixed;inset:0;z-index:0;pointer-events:none}

/* ══════════════════════════ NAV ══════════════════════════ */
#phet-stage {
    position: absolute; top: 0; left: 0;
    width: 1280px; height: 720px;
    background: var(--bg);
    display: flex; flex-direction: column;
    overflow: hidden; transform-origin: 0 0;
    box-shadow: 0 0 50px rgba(0, 0, 0, 0.4);
    touch-action: none;
}

.euler-nav{
    position:absolute;top:0;left:0;right:0;height:58px;
    display:flex;align-items:center;justify-content:space-between;
    padding:0 2rem;
    background:rgba(6,8,16,0.92);
    backdrop-filter:blur(20px);
    border-bottom:1px solid var(--border);
    z-index:200;
}
.nav-logo a{text-decoration:none;font-weight:800;font-size:1.15rem;color:var(--text);display:flex;align-items:center;gap:0.4rem}
.nav-logo em{color:var(--primary);font-style:normal}
.nav-center{font-size:0.85rem;color:var(--muted);letter-spacing:0.5px;font-weight:500}
.nav-back{display:flex;align-items:center;gap:0.4rem;padding:0.45rem 1.1rem;border-radius:50px;border:1px solid var(--border);background:transparent;color:var(--text);font-size:0.82rem;text-decoration:none;transition:0.2s}
.nav-back:hover{border-color:var(--primary);color:var(--primary)}

/* ══════════════════════════ APP SHELL ══════════════════════════ */
.app-shell{
    position:absolute;top:58px;bottom:0;left:0;right:0;
    display:grid;
    grid-template-columns:520px 1fr;
    z-index:1;
}

/* ══════════════════════════ STORY PANEL ══════════════════════════ */
.story-panel{
    display:flex;flex-direction:column;
    background:var(--surface);
    border-right:1px solid var(--border);
    overflow:hidden;
}

/* Progress bar */
.progress-bar-wrap{height:4px;background:var(--surface2);flex-shrink:0}
.progress-bar-fill{height:100%;background:linear-gradient(90deg,var(--primary),var(--gold));width:0%;transition:width 0.5s ease;border-radius:0 4px 4px 0}

/* Content */
.story-content{flex:1;overflow-y:auto;padding:2.5rem 2.5rem 1rem;scroll-behavior:smooth}
.story-content::-webkit-scrollbar{width:4px}
.story-content::-webkit-scrollbar-thumb{background:var(--surface2);border-radius:4px}

/* Step cards */
.step-block{display:none;flex-direction:column;gap:1.4rem;animation:slideIn 0.4s ease}
.step-block.active{display:flex}

@keyframes slideIn{from{opacity:0;transform:translateY(16px)}to{opacity:1;transform:translateY(0)}}

.step-kicker{
    display:inline-flex;align-items:center;gap:0.5rem;
    background:rgba(99,102,241,0.12);
    border:1px solid rgba(99,102,241,0.25);
    border-radius:50px;
    padding:0.3rem 1rem;
    font-size:0.75rem;font-weight:700;text-transform:uppercase;letter-spacing:1px;
    color:var(--primary);width:fit-content;
}

.step-block h2{font-size:1.7rem;font-weight:900;line-height:1.2;color:white}
.step-block h2 span{color:var(--gold)}

.step-block p{color:#94a3b8;line-height:1.8;font-size:0.98rem}
.step-block p strong{color:white;font-weight:700}
.step-block p .hl{color:var(--gold);font-family:'JetBrains Mono';font-weight:700;background:rgba(250,204,21,0.08);padding:0.1em 0.3em;border-radius:4px}
.step-block p .real{color:var(--green);font-weight:700}
.step-block p .imag{color:var(--pink);font-weight:700}

/* Equation display boxes */
.eq{
    background:var(--surface2);
    border:1px solid var(--border);
    border-radius:16px;
    padding:1.2rem 1.6rem;
    font-family:'JetBrains Mono',monospace;
    font-size:1.15rem;
    color:white;
    line-height:2;
}
.eq.center{text-align:center}
.eq.gold{border-color:rgba(250,204,21,0.4);background:rgba(250,204,21,0.06);color:var(--gold);font-size:1.4rem;text-align:center}
.eq.purple{border-color:rgba(99,102,241,0.4);background:rgba(99,102,241,0.07);color:#818cf8;text-align:center}
.eq small{display:block;font-family:'Outfit';font-size:0.75rem;color:var(--muted);margin-top:0.4rem;letter-spacing:0.5px}

/* Hint blocks */
.hint{background:rgba(99,102,241,0.06);border:1px dashed rgba(99,102,241,0.3);border-radius:12px;padding:0.9rem 1.2rem;font-size:0.88rem;color:#818cf8;display:flex;gap:0.7rem;align-items:flex-start}
.hint i{margin-top:2px;flex-shrink:0}

/* Colour legend */
.color-legend{display:flex;flex-direction:column;gap:0.5rem}
.cl-item{display:flex;align-items:center;gap:0.8rem;font-size:0.9rem;color:#94a3b8}
.cl-dot{width:12px;height:12px;border-radius:50%;flex-shrink:0}

/* ── Story Footer ── */
.story-footer{display:flex;align-items:center;gap:1rem;padding:1.2rem 2.5rem 3.5rem;border-top:1px solid var(--border);flex-shrink:0}
.step-pips{display:flex;gap:6px;flex:1;justify-content:center}
.pip{width:7px;height:7px;border-radius:50%;background:var(--muted);cursor:pointer;transition:0.3s;border:none;padding:0}
.pip.active{background:var(--primary);transform:scale(1.5)}
.pip:hover{background:var(--primary)}

.nav-btn{display:flex;align-items:center;gap:0.5rem;padding:0.65rem 1.4rem;border-radius:50px;font-family:'Outfit';font-weight:700;font-size:0.9rem;cursor:pointer;transition:0.2s;border:none}
.nav-btn.ghost{background:transparent;border:1px solid var(--border);color:var(--text)}
.nav-btn.ghost:hover:not(:disabled){border-color:rgba(255,255,255,0.3);background:rgba(255,255,255,0.05)}
.nav-btn.primary{background:var(--primary);color:white;box-shadow:0 0 20px rgba(99,102,241,0.4)}
.nav-btn.primary:hover{background:#4f46e5;box-shadow:0 0 30px rgba(99,102,241,0.6)}
.nav-btn:disabled{opacity:0.3;cursor:default}
.nav-btn.gold-btn{background:var(--gold);color:#000}

/* ══════════════════════════ VISUAL SHELL ══════════════════════════ */
.visual-shell{display:flex;flex-direction:column;align-items:center;justify-content:center;padding:1.5rem;gap:1rem;background:var(--bg);overflow:hidden}

#mainCanvas{border-radius:20px;border:1px solid var(--border);background:var(--surface);max-width:100%;max-height:100%}

.canvas-caption{font-size:0.82rem;color:var(--muted);text-align:center;max-width:480px;line-height:1.6;min-height:2.5em;transition:opacity 0.3s}

/* Slider */
.slider-row{display:flex;align-items:center;gap:1rem;width:100%;max-width:480px}
.slider-row label{font-size:0.85rem;color:var(--text);font-weight:600;white-space:nowrap}
.euler-slider{flex:1;height:5px;appearance:none;background:var(--surface2);border-radius:10px;outline:none;cursor:pointer}
.euler-slider::-webkit-slider-thumb{appearance:none;width:20px;height:20px;background:var(--primary);border-radius:50%;border:2px solid white;cursor:pointer;box-shadow:0 0 12px rgba(99,102,241,0.7)}
.slider-val{font-family:'JetBrains Mono';font-size:0.85rem;color:var(--gold);min-width:55px;text-align:right}

/* Chips */
.chip-row{display:flex;gap:0.7rem;flex-wrap:wrap;justify-content:center;max-width:500px}
.chip{background:var(--surface);border:1px solid var(--border);border-radius:12px;padding:0.5rem 1rem;font-size:0.82rem;display:flex;flex-direction:column;gap:0.2rem;align-items:center;min-width:90px}
.chip-label{color:var(--muted);font-size:0.72rem;text-transform:uppercase;letter-spacing:0.5px;font-weight:600}
.chip-val{font-family:'JetBrains Mono';font-size:0.95rem;font-weight:700;color:white;text-align:center}
.chip.gold-chip{border-color:rgba(250,204,21,0.4);background:rgba(250,204,21,0.07)}
.chip.gold-chip .chip-val{color:var(--gold)}

/* ══════════════════════════ FINALE OVERLAY ══════════════════════════ */
.finale-overlay{position:absolute;inset:0;background:rgba(0,0,0,0.88);z-index:500;display:flex;align-items:center;justify-content:center;opacity:0;pointer-events:none;transition:opacity 0.6s;backdrop-filter:blur(12px)}
.finale-overlay.show{opacity:1;pointer-events:all}

.finale-card{position:relative;background:var(--surface);border:1px solid rgba(250,204,21,0.25);border-radius:30px;padding:3.5rem 4rem;text-align:center;max-width:560px;overflow:hidden;animation:popUp 0.6s cubic-bezier(0.34,1.56,0.64,1) both}

@keyframes popUp{from{transform:scale(0.7);opacity:0}to{transform:scale(1);opacity:1}}

/* Rings */
.finale-rings{position:absolute;inset:0;pointer-events:none}
.ring{position:absolute;border-radius:50%;border:1px solid;top:50%;left:50%;transform:translate(-50%,-50%);animation:expand 3s ease-in-out infinite}
.ring1{width:200px;height:200px;border-color:rgba(250,204,21,0.15);animation-delay:0s}
.ring2{width:340px;height:340px;border-color:rgba(250,204,21,0.08);animation-delay:0.8s}
.ring3{width:480px;height:480px;border-color:rgba(250,204,21,0.04);animation-delay:1.6s}
@keyframes expand{0%,100%{transform:translate(-50%,-50%) scale(1);opacity:0.8}50%{transform:translate(-50%,-50%) scale(1.05);opacity:0.3}}

.finale-kicker{font-size:0.78rem;color:var(--muted);text-transform:uppercase;letter-spacing:2px;margin-bottom:1.5rem;position:relative}
.finale-eq{font-size:4.5rem;font-weight:900;color:var(--gold);font-family:'JetBrains Mono';text-shadow:0 0 80px rgba(250,204,21,0.6);position:relative;margin-bottom:2rem;line-height:1}
.finale-constants{display:flex;justify-content:center;gap:1.5rem;margin-bottom:1.5rem;position:relative;flex-wrap:wrap}
.fc{font-size:0.85rem;color:var(--muted);display:flex;align-items:center;gap:0.3rem;font-weight:600}
.finale-desc{color:#64748b;font-size:0.9rem;line-height:1.7;max-width:400px;margin:0 auto 2rem;position:relative}
.finale-btn{display:inline-flex;align-items:center;gap:0.6rem;padding:0.9rem 2.5rem;border-radius:50px;border:2px solid var(--gold);background:transparent;color:var(--gold);font-family:'Outfit';font-weight:700;font-size:1rem;cursor:pointer;transition:0.3s;position:relative}
.finale-btn:hover{background:var(--gold);color:#000}

sup,sub{line-height:0}

/* Media Query to keep footer compact on mobile */
@media screen and (max-width: 899px) {
    .story-footer {
        padding: 1.2rem 2.5rem !important;
    }
}