/* ==========================================================
   BACK TO TOP BUTTON - HYBRID "RETURN TO ZERO" PROTOCOL
   React state management + Industrial mustard styling
   ========================================================== */

.back-to-top {
  /* Positioning - Fixed bottom-right corner, ABOVE sticky header */
  position: fixed;
  bottom: 25px;
  right: 20px;
  z-index: 10000; /* Above sticky header (9999) - Exit always accessible */
  
  /* Size - 60px diameter for 55" display + mobile optimization */
  width: 60px;
  height: 60px;
  
  /* Visual - High-visibility Mustard "Signal" indicator */
  background: rgba(232, 155, 60, 0.2); /* Mustard with 20% opacity */
  border: 2px solid rgba(232, 155, 60, 0.8);
  border-radius: 50%; /* Circular */
  
  /* Shadow - Industrial floating control aesthetic */
  box-shadow: 
    0 4px 12px rgba(0, 0, 0, 0.6),
    0 0 20px rgba(232, 155, 60, 0.3);
  
  /* Interaction */
  cursor: pointer;
  transition: opacity 0.4s ease, visibility 0.4s ease, transform 0.2s ease;
  
  /* Content centering */
  display: flex;
  align-items: center;
  justify-content: center;
  
  /* Initial state - hidden */
  opacity: 0;
  visibility: hidden;
}

/* Visible state - triggered by React useState after 800px scroll */
.back-to-top.visible {
  opacity: 1;
  visibility: visible;
}

/* Hover state - Brighter "Machine Control" signal */
.back-to-top:hover {
  background: rgba(232, 155, 60, 0.35);
  border-color: rgba(232, 155, 60, 1);
  box-shadow: 
    0 6px 16px rgba(0, 0, 0, 0.7),
    0 0 30px rgba(232, 155, 60, 0.5);
  transform: translateY(-2px);
}

/* Active state - Mechanical feedback (scale down) */
.back-to-top:active {
  transform: scale(0.9);
  box-shadow: 
    0 2px 8px rgba(0, 0, 0, 0.5),
    0 0 15px rgba(232, 155, 60, 0.4);
}

/* SVG Icon - Crisp 4K rendering on 55" display */
.back-to-top svg {
  width: 24px;
  height: 24px;
  fill: none;
  stroke: rgba(232, 155, 60, 1); /* Mustard stroke */
  stroke-width: 3;
  stroke-linecap: square; /* Industrial aesthetic */
  transition: stroke 0.3s ease;
}

.back-to-top:hover svg {
  stroke: rgba(232, 155, 60, 1); /* Full brightness on hover */
}

/* Mobile adjustments - Maintain 60px for thumb accessibility */
@media (max-width: 768px) {
  .back-to-top {
    width: 56px;
    height: 56px;
    bottom: 20px;
    right: 20px;
  }
  
  .back-to-top svg {
    width: 22px;
    height: 22px;
  }
}

/* Accessibility - Focus state for keyboard navigation */
.back-to-top:focus {
  outline: 2px solid rgba(232, 155, 60, 1);
  outline-offset: 2px;
}

/* Small screens - Maintain visibility without interference */
@media (max-height: 600px) {
  .back-to-top {
    bottom: 16px;
    right: 16px;
    width: 52px;
    height: 52px;
  }
  
  .back-to-top svg {
    width: 20px;
    height: 20px;
  }
}

/* High DPI displays - Ensure crisp rendering on 4K 55" */
@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi) {
  .back-to-top svg {
    stroke-width: 2.5; /* Slightly thinner on high-DPI to prevent boldness */
  }
}