* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html, body {
  background: #f0f0f0;
  font-family: "PingFang SC", -apple-system, BlinkMacSystemFont, "Helvetica Neue", Arial, sans-serif;
}

.portfolio {
  display: flex;
  flex-direction: column;
  align-items: center;
  width: 100%;
}

.portfolio img {
  display: block;
  width: 100%;
  max-width: 1920px;
  height: auto;
}

.back-btn {
  position: fixed;
  top: 24px;
  left: 24px;
  z-index: 100;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px 10px 14px;
  background: rgba(20, 20, 24, 0.72);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid rgba(255, 255, 255, 0.12);
  border-radius: 999px;
  color: #fff;
  font-size: 15px;
  font-weight: 500;
  text-decoration: none;
  box-shadow: 0 6px 20px rgba(0, 0, 0, 0.25);
  transition: transform 0.15s ease, background 0.15s ease, box-shadow 0.15s ease;
}

.back-btn:hover {
  background: rgba(66, 37, 177, 0.9);
  transform: translateX(-2px);
  box-shadow: 0 8px 24px rgba(66, 37, 177, 0.45);
}

.back-btn svg {
  width: 16px;
  height: 16px;
  flex-shrink: 0;
}