/* ═══════════════════════════════════════════
   RESET & ROOT
═══════════════════════════════════════════ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --navy:         #17263C;
  --amber:        #C17826;
  --amber-dk:     #A5631A;
  --amber-lt:     #FDF3E3;
  --amber-bd:     #DFA540;
  --linen:        #ECEAE2;
  --white:        #FFFFFF;
  --border:       #D3CEC5;
  --text:         #1A1A1A;
  --mid:          #47423D;
  --muted:        #7A756D;
  --s-text:       rgba(255,255,255,0.87);
  --s-dim:        rgba(255,255,255,0.40);
  --s-hover:      rgba(255,255,255,0.07);
  --s-active:     rgba(193,120,38,0.22);
  --error:        #B53232;
  --sw: 270px;
}

html, body {
  height: 100%;
  font-family: 'Vazirmatn', sans-serif;
  background: var(--linen);
  color: var(--text);
  -webkit-font-smoothing: antialiased;
}

/* ═══════════════════════════════════════════
   APP SHELL
═══════════════════════════════════════════ */
.app {
  display: flex;
  height: 100vh;
  overflow: hidden;
}

/* ═══════════════════════════════════════════
   SIDEBAR
   Signature element: repeating diagonal
   thread lines on the navy background,
   evoking the look of woven fabric.
═══════════════════════════════════════════ */
.sidebar {
  width: var(--sw);
  flex-shrink: 0;
  background: var(--navy);
  background-image: repeating-linear-gradient(
    -56deg,
    transparent 0px,     transparent 9px,
    rgba(255,255,255,.03) 9px, rgba(255,255,255,.03) 10px
  );
  display: flex;
  flex-direction: column;
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: rgba(255,255,255,.12) transparent;
}
.sidebar::-webkit-scrollbar       { width: 3px; }
.sidebar::-webkit-scrollbar-thumb { background: rgba(255,255,255,.15); }

/* Brand header */
.s-head {
  padding: 22px 16px 18px;
  border-bottom: 1px solid rgba(255,255,255,.07);
  flex-shrink: 0;
}
.brand {
  display: flex;
  align-items: center;
  gap: 11px;
}
.brand-mark {
  width: 37px;
  height: 37px;
  background: var(--bg-primary);
  border-radius: 9px;
  flex-shrink: 0;
  display: flex;
  align-items: center;
  justify-content: center;
}
<!-- .brand-mark svg { width: 21px; height: 21px; } -->
.brand-mark img { width: 31px; height: 31px; }
.brand-name { font-size: 14px; font-weight: 700; color: #fff; line-height: 1.3; }
.brand-sub  { font-size: 10.5px; color: var(--s-dim); margin-top: 3px; }

/* Nav */
#nav { flex: 1; padding: 4px 0 20px; }

.cat-sec { padding-top: 8px; }

/* Category heading with trailing line */
.cat-head {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 10px 16px 6px;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 1.1px;
  color: var(--amber);
}
.cat-head::after {
  content: '';
  flex: 1;
  height: 1px;
  background: rgba(255,255,255,.07);
}

/* Formula buttons */
.f-btn {
  display: block;
  width: 100%;
  text-align: right;
  background: none;
  border: none;
  border-right: 3px solid transparent;
  font-family: 'Vazirmatn', sans-serif;
  font-size: 12.5px;
  color: var(--s-text);
  padding: 9px 14px 9px 12px;
  cursor: pointer;
  line-height: 1.45;
  transition: background 0.1s;
}
.f-btn:hover { background: var(--s-hover); }
.f-btn.active {
  background: var(--s-active);
  color: #fff;
  font-weight: 600;
  border-right-color: var(--amber);
}

/* ═══════════════════════════════════════════
   CONTENT AREA
═══════════════════════════════════════════ */
.content {
  flex: 1;
  overflow-y: auto;
  display: flex;
  flex-direction: column;
  padding: 40px 48px;
  scrollbar-width: thin;
  scrollbar-color: var(--border) transparent;
}
.content::-webkit-scrollbar       { width: 4px; }
.content::-webkit-scrollbar-thumb { background: var(--border); border-radius: 4px; }

/* Welcome / idle state */
.welcome {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  gap: 10px;
}
.welcome-glyph { font-size: 56px; opacity: .15; line-height: 1; margin-bottom: 6px; }
.welcome h2 { font-size: 17px; font-weight: 600; color: var(--mid); opacity: .65; }
.welcome p  { font-size: 13px; color: var(--muted); }
.welcome h5 { position: fixed; bottom: 18px; left: 18px; font-size: 11px; font-weight: 400; color: var(--muted);}

/* ── Formula card ─────────────────────── */
.f-card {
  background: var(--white);
  border-radius: 14px;
  padding: 32px 36px 36px;
  box-shadow: 0 1px 4px rgba(0,0,0,.05), 0 8px 28px rgba(0,0,0,.05);
  max-width: 520px;
  width: 100%;
}

.f-tag {
  display: inline-block;
  padding: 3px 13px;
  border-radius: 100px;
  background: var(--amber-lt);
  border: 1px solid var(--amber-bd);
  color: var(--amber-dk);
  font-size: 11px;
  font-weight: 700;
  margin-bottom: 14px;
  letter-spacing: .3px;
}

.f-title {
  font-size: 19px;
  font-weight: 700;
  line-height: 1.55;
  color: var(--text);
  margin-bottom: 28px;
}

/* ── Inputs ───────────────────────────── */
.inp-row { margin-bottom: 15px; }

.inp-lbl {
  display: block;
  font-size: 12.5px;
  font-weight: 500;
  color: var(--muted);
  margin-bottom: 7px;
}

.inp {
  width: 100%;
  padding: 11px 14px;
  background: #F6F4F0;
  border: 1.5px solid var(--border);
  border-radius: 8px;
  font-family: 'Vazirmatn', sans-serif;
  font-size: 15px;
  color: var(--text);
  direction: ltr;
  text-align: left;
  /* Remove spinner arrows */
  -moz-appearance: textfield;
  appearance: textfield;
  transition: border-color .12s, box-shadow .12s, background .12s;
}
.inp::-webkit-inner-spin-button,
.inp::-webkit-outer-spin-button { -webkit-appearance: none; }
.inp::placeholder { color: #C5C1BB; }
.inp:focus {
  outline: none;
  background: #fff;
  border-color: var(--amber);
  box-shadow: 0 0 0 3px rgba(193,120,38,.13);
}
.inp.err { border-color: var(--error); background: #fff8f8; }

select.inp {
  cursor: pointer;
  direction: rtl;
  text-align: right;
}

/* ── Calculate button ─────────────────── */
.calc-btn {
  display: block;
  width: 100%;
  margin-top: 24px;
  padding: 13px;
  background: var(--amber);
  color: #fff;
  border: none;
  border-radius: 8px;
  font-family: 'Vazirmatn', sans-serif;
  font-size: 15px;
  font-weight: 700;
  cursor: pointer;
  letter-spacing: .4px;
  transition: background .11s, transform .07s;
}
.calc-btn:hover  { background: var(--amber-dk); }
.calc-btn:active { transform: scale(.985); }

/* ── Error message ────────────────────── */
.err-msg {
  margin-top: 10px;
  font-size: 12.5px;
  color: var(--error);
  display: none;
}
.err-msg.show { display: block; }

/* ── Result box ───────────────────────── */
.res-box {
  margin-top: 22px;
  background: var(--amber-lt);
  border: 1.5px solid var(--amber-bd);
  border-radius: 10px;
  padding: 16px 22px;
  display: none;
  flex-direction: row;
  align-items: baseline;
  gap: 10px;
}
.res-box.show {
  display: flex;
  animation: fadeUp .22s ease;
}

.res-lbl  { font-size: 11.5px; font-weight: 500; color: var(--amber-dk); flex-shrink: 0; }
.res-val  { font-size: 30px; font-weight: 800; color: var(--amber); flex: 1; }
.res-unit { font-size: 12px; font-weight: 500; color: var(--amber-dk); opacity: .85; flex-shrink: 0; }

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(5px); }
  to   { opacity: 1; transform: translateY(0);   }
}

/* ═══════════════════════════════════════════
   HAMBURGER BUTTON — mobile only
═══════════════════════════════════════════ */
.hamburger {
  display: none;
  position: fixed;
  top: 14px;
  right: 14px;
  z-index: 60;
  width: 42px;
  height: 42px;
  background: var(--navy);
  border: none;
  border-radius: 9px;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
  cursor: pointer;
  box-shadow: 0 2px 10px rgba(0,0,0,.18);
}
.hamburger span {
  display: block;
  width: 19px;
  height: 2px;
  background: #fff;
  border-radius: 2px;
  transition: transform .22s ease, opacity .22s ease;
}
/* Morph into an X when the drawer is open */
.hamburger.open span:nth-child(1) { transform: translateY(6px) rotate(45deg); }
.hamburger.open span:nth-child(2) { opacity: 0; }
.hamburger.open span:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }

/* ═══════════════════════════════════════════
   OVERLAY — dim backdrop behind drawer
═══════════════════════════════════════════ */
.overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.4);
  z-index: 45;
  opacity: 0;
  transition: opacity .22s ease;
}
.overlay.show {
  display: block;
  opacity: 1;
}

/* ═══════════════════════════════════════════
   RESPONSIVE — narrow screens (drawer menu)
═══════════════════════════════════════════ */
@media (max-width: 720px) {
  .hamburger { display: flex; }

  .app {
    height: 100vh;
  }

  /* Sidebar becomes a fixed slide-in panel from the right */
  .sidebar {
    position: fixed;
    top: 0;
    right: 0;
    height: 100vh;
    width: 78vw;
    max-width: 300px;
    z-index: 50;
    transform: translateX(100%);
    transition: transform .25s ease;
    box-shadow: -6px 0 24px rgba(0,0,0,.25);
  }
  .sidebar.open {
    transform: translateX(0);
  }

  .s-head { padding: 18px 16px 16px; }

  .content {
    width: 100%;
    padding: 72px 18px 24px;
  }
  .f-card  { padding: 20px; max-width: 100%; border-radius: 10px; }
  .f-title { font-size: 16px; margin-bottom: 20px; }
}