*, *::before, *::after { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  font-size: 14px;
  background: #f6f8fa;
  color: #24292f;
  height: 100vh;
  display: flex;
  flex-direction: column;
}

header {
  padding: 0.75rem 1.5rem;
  background: #24292f;
  color: #fff;
  display: flex;
  align-items: baseline;
  gap: 1rem;
  flex-shrink: 0;
}
header h1 { margin: 0; font-size: 1.1rem; }
header p  { margin: 0; font-size: 0.85rem; color: #8b949e; }

main {
  display: flex;
  flex: 1;
  overflow: hidden;
  gap: 0;
}

/* ── Editor panel ── */
.editor-panel {
  display: flex;
  flex-direction: column;
  width: var(--editor-width, 50%);
  min-width: 15%;
  max-width: 85%;
  background: #fff;
}

/* ── Resize handle ── */
.resize-handle {
  width: 5px;
  background: #d0d7de;
  cursor: col-resize;
  flex-shrink: 0;
  transition: background 0.15s;
}
.resize-handle:hover,
.resize-handle.dragging {
  background: #0969da;
}

.toolbar {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.5rem 0.75rem;
  border-bottom: 1px solid #d0d7de;
  background: #f6f8fa;
  flex-shrink: 0;
}
.spacer { flex: 1; }

#editor {
  flex: 1;
  resize: none;
  border: none;
  outline: none;
  padding: 1rem;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 13px;
  line-height: 1.6;
  color: #24292f;
  background: #fff;
}

/* ── Preview panel ── */
.preview-panel {
  display: flex;
  flex-direction: column;
  flex: 1;
  overflow-y: auto;
  background: #fff;
}

.preview-label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: #8b949e;
  padding: 0.5rem 1rem;
  border-bottom: 1px solid #d0d7de;
  background: #f6f8fa;
  flex-shrink: 0;
}

#preview {
  padding: 1.5rem 2rem;
  flex: 1;
}

/* ── Buttons ── */
.btn {
  padding: 0.3rem 0.75rem;
  font-size: 13px;
  border-radius: 6px;
  border: 1px solid;
  cursor: pointer;
  white-space: nowrap;
  transition: background 0.1s;
}
.btn-primary {
  background: #2da44e;
  border-color: rgba(27,31,36,0.15);
  color: #fff;
}
.btn-primary:hover { background: #2c974b; }
.btn-secondary {
  background: #f6f8fa;
  border-color: rgba(27,31,36,0.15);
  color: #24292f;
}
.btn-secondary:hover { background: #eaeef2; }

/* File button styled as button */
.file-btn {
  display: inline-flex;
  align-items: center;
  padding: 0.3rem 0.75rem;
  font-size: 13px;
  border-radius: 6px;
  border: 1px solid rgba(27,31,36,0.15);
  background: #f6f8fa;
  color: #24292f;
  cursor: pointer;
}
.file-btn:hover { background: #eaeef2; }
.file-btn input { display: none; }

/* ── Toast ── */
.toast {
  position: fixed;
  bottom: 1.5rem;
  left: 50%;
  transform: translateX(-50%) translateY(2rem);
  background: #24292f;
  color: #fff;
  padding: 0.5rem 1.25rem;
  border-radius: 6px;
  font-size: 13px;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.2s, transform 0.2s;
  z-index: 100;
}
.toast.show {
  opacity: 1;
  transform: translateX(-50%) translateY(0);
}

/* ─── Mobile tabs (hidden on desktop) ─── */
.mobile-tabs {
  display: none;
}

/* ─── Tablet: iPad Pro 11" portrait (≤834px) ─── */
@media (max-width: 834px) {
  header {
    padding: 0 1rem;
  }
  header h1 {
    font-size: 0.95rem;
  }
  .toolbar {
    gap: 0.3rem;
  }
  .btn {
    padding: 0.3rem 0.55rem;
    font-size: 12px;
  }
  .file-btn {
    padding: 0.3rem 0.55rem;
    font-size: 12px;
  }
  .resize-handle {
    width: 6px;
  }
  #editor {
    padding: 0.75rem;
  }
  #preview {
    padding: 1rem 1.25rem;
  }
}

/* ─── Mobile: iPhone Pro Max (≤430px) ─── */
@media (max-width: 430px) {
  header {
    padding: 0 0.75rem;
  }
  header h1 {
    font-size: 0.85rem;
  }
  .toolbar {
    gap: 0.2rem;
    flex-wrap: wrap;
    justify-content: flex-end;
  }
  .btn {
    padding: 0.3rem 0.45rem;
    font-size: 11px;
  }
  .file-btn {
    padding: 0.3rem 0.45rem;
    font-size: 11px;
  }

  .mobile-tabs {
    display: flex;
    flex-shrink: 0;
    background: #f6f8fa;
    border-bottom: 1px solid rgba(27,31,36,0.15);
  }
  .mobile-tab {
    flex: 1;
    padding: 0.6rem 0;
    background: none;
    border: none;
    border-bottom: 2px solid transparent;
    font-size: 14px;
    font-weight: 500;
    color: #57606a;
    cursor: pointer;
    transition: color 0.15s, border-color 0.15s;
  }
  .mobile-tab.active {
    color: #0969da;
    border-bottom-color: #0969da;
  }

  main {
    flex-direction: column;
    overflow: hidden;
  }
  .editor-panel {
    width: 100% !important;
    min-width: 0 !important;
    max-width: 100% !important;
    flex: 1;
    display: flex;
    flex-direction: column;
  }
  .editor-panel.mobile-hidden {
    display: none;
  }
  .preview-panel {
    width: 100% !important;
    min-width: 0 !important;
    flex: 1;
    display: none;
  }
  .preview-panel.mobile-visible {
    display: flex;
    flex-direction: column;
  }
  .resize-handle {
    display: none;
  }
  #editor {
    padding: 0.75rem;
    font-size: 15px;
  }
  #preview {
    padding: 1rem;
  }
  .preview-label {
    display: none;
  }
  .toast {
    left: 1rem;
    right: 1rem;
    bottom: 1rem;
    transform: none;
  }
  .toast.show {
    transform: none;
  }
}