/* ── NEWTON'S LAWS SIMULATOR ─────────────────────────────────────────────── */

:root {
    --bg: #ffffff;
    --surface: #f0f0f0;
    --card: #e0e0e0;
    --dark: rgb(59,68,83);
    --text: #1a1a1a;
    --muted: #666;
    --sky: #78dbff;
    --ground: #4caf50;
}

* { margin:0; padding:0; box-sizing:border-box; }
html, body { height:100%; }

body {
    background: var(--bg);
    color: var(--text);
    font-family: "Poppins", sans-serif;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 2rem 1rem 3rem;
}

nav {
    position: fixed; top:0; left:0;
    width:100vw; height:8vh;
    display:flex; justify-content:space-between; align-items:center;
    padding: 0 2rem;
    background-color: rgba(255,255,255,0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-bottom: 1px solid rgba(0,0,0,0.07);
    z-index:100;
}

.nav-logo { font-size:2.5vh; cursor:default; }

.nav-back a {
    font-size:2vh; color:var(--text); text-decoration:none;
    position:relative; padding-bottom:2px;
}

.nav-back a::after {
    content:''; position:absolute; bottom:-2px; left:0;
    width:0%; height:1.5px; background:var(--text);
    transition: width 0.25s ease;
}

.nav-back a:hover::after { width:100%; }

header { text-align:center; margin-top:10vh; margin-bottom:1.5rem; }

header h1 {
    font-family:"Pixelify Sans", sans-serif;
    font-weight:400; font-size:clamp(2rem,5vw,3.5rem);
    color: var(--text);
}

header p { font-size:1.8vh; color:var(--muted); margin-top:0.3rem; }

.sim-wrapper { width:100%; max-width:920px; display:flex; flex-direction:column; gap:1rem; }

/* MODE TABS */
.mode-tabs { display:flex; gap:0.6rem; flex-wrap:wrap; }

.mode-tab {
    padding:0.5rem 1.2rem; border:none; border-radius:0.7rem;
    background:var(--card); color:var(--muted);
    font-family:"Poppins",sans-serif; font-size:1.5vh;
    cursor:pointer; transition:all 0.2s ease;
    box-shadow:0 1px 4px rgba(0,0,0,0.06);
}

.mode-tab.active { background:var(--dark); color:#fff; }
.mode-tab:hover  { transform:translateY(-2px); box-shadow:0 6px 16px rgba(0,0,0,0.10); }

/* CONTROLS */
.controls { display:grid; grid-template-columns:repeat(4,1fr); gap:0.8rem; }
.controls.hidden { display:none; }

.control-group {
    background:var(--surface); border-radius:1rem;
    padding:1rem; box-shadow:0 1px 4px rgba(0,0,0,0.06);
}

.control-group label { display:block; font-size:1.3vh; color:var(--muted); margin-bottom:0.3rem; }
.control-group .val  { font-family:"Pixelify Sans",sans-serif; font-size:2.2vh; margin-bottom:0.5rem; color:var(--text); }

input[type="range"] {
    width:100%; appearance:none; -webkit-appearance:none;
    height:3px; background:rgba(0,0,0,0.12); border-radius:2px; outline:none;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance:none; appearance:none;
    width:14px; height:14px; background:var(--dark);
    border-radius:50%; cursor:pointer;
}

input[type="range"]::-moz-range-thumb {
    width:14px; height:14px; background:var(--dark);
    border-radius:50%; cursor:pointer; border:none;
}

/* CANVAS */
.canvas-wrap {
    position:relative; border-radius:1rem; overflow:hidden;
    background:#f5f0e8; box-shadow:0 2px 8px rgba(0,0,0,0.10);
}

canvas { display:block; width:100%; }

/* STATS */
.stats { display:flex; gap:0.8rem; flex-wrap:wrap; }

.stat {
    background:var(--surface); border-radius:1rem;
    padding:0.8rem 1rem; box-shadow:0 1px 4px rgba(0,0,0,0.06);
    flex:1; min-width:120px;
}

.stat-label { font-size:1.3vh; color:var(--muted); margin-bottom:0.2rem; }
.stat-value { font-family:"Pixelify Sans",sans-serif; font-size:2.2vh; color:var(--text); }
.stat-unit  { font-family:"Poppins",sans-serif; font-size:1.1vh; color:var(--muted); margin-left:0.1rem; }

/* FORMULA BOX */
.formula-box {
    background:var(--surface); border-radius:1rem;
    padding:1rem 1.2rem; display:grid;
    grid-template-columns:1fr 1fr; gap:0.4rem 2rem;
    box-shadow:0 1px 4px rgba(0,0,0,0.06);
    font-size:1.5vh; color:var(--muted);
}

.formula-box span { color:var(--dark); font-weight:500; }

@media (max-width:700px) {
    .controls      { grid-template-columns:1fr 1fr; }
    .formula-box   { grid-template-columns:1fr; }
    .mode-tab      { font-size:1.2vh; padding:0.4rem 0.8rem; }
}

/* ACTION BUTTONS */
.action-row { display:flex; gap:0.8rem; }
.action-row.hidden { display:none; }

.action-btn {
    flex:1; padding:0.8rem; border:none; border-radius:1rem;
    background:var(--card); color:var(--text);
    font-family:"Poppins",sans-serif; font-size:1.8vh;
    cursor:pointer;
    transition:transform 0.22s ease, box-shadow 0.22s ease, background 0.22s ease;
    box-shadow:0 1px 4px rgba(0,0,0,0.06);
}
.action-btn:hover { transform:translateY(-3px) scale(1.015); box-shadow:0 8px 20px rgba(0,0,0,0.10); background:#d4d4d4; }
.action-btn.primary { background:var(--dark); color:#fff; }
.action-btn.primary:hover { background:rgb(45,52,65); color:#fff; }