/* === 基础按钮 === */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-6);
  font-family: var(--font-family-primary);
  font-size: var(--text-base);
  font-weight: var(--font-semibold);
  line-height: var(--leading-tight);
  text-decoration: none;
  border: none;
  border-radius: 50px;
  cursor: pointer;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
  letter-spacing: 0.5px;
}

/* 内层上移：外层 .btn 保持原有几何命中区，避免下沿悬停抖动 */
.btn .btn-shift {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-width: 0;
  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.btn:before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.3), transparent);
  transition: left 0.6s;
}

.btn:hover:before {
  left: 100%;
}

.btn::after {
  content: '';
  position: absolute;
  inset: 0;
  border-radius: 50px;
  padding: 2px;
  background: linear-gradient(135deg, rgba(255,255,255,0.4), transparent);
  -webkit-mask: linear-gradient(#fff 0 0) content-box, linear-gradient(#fff 0 0);
  -webkit-mask-composite: xor;
  mask-composite: exclude;
  opacity: 0;
  transition: opacity 0.3s ease;
}

.btn:hover::after {
  opacity: 1;
}

/* === 主要按钮 === */
.btn-primary {
  background: var(--gradient-primary);
  color: var(--neutral-white);
  box-shadow: 0 10px 30px rgba(0, 149, 255, 0.4);
}

.btn-primary:hover {
  box-shadow: 0 15px 40px rgba(0, 212, 255, 0.6);
  background: linear-gradient(70deg, #00D4FF 0%, #0095FF 100%);
}

.btn-primary:hover > .btn-shift {
  transform: translateY(-3px);
}

.btn-primary:active > .btn-shift {
  transform: translateY(-1px);
}

.btn-primary:active {
  box-shadow: 0 5px 20px rgba(0, 149, 255, 0.4);
}

/* === 毛玻璃按钮 === */
.btn-glass {
  background: rgba(255, 255, 255, 0.15);
  backdrop-filter: blur(10px);
  border: 2px solid rgba(255, 255, 255, 0.3);
  color: var(--neutral-white);
  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
}

.btn-glass:hover {
  background: rgba(255, 255, 255, 0.25);
  border-color: rgba(255, 255, 255, 0.5);
  box-shadow: 0 12px 40px rgba(255, 255, 255, 0.2);
}

.btn-glass:hover > .btn-shift {
  transform: translateY(-3px);
}

.btn-glass:active > .btn-shift {
  transform: translateY(-1px);
}

/* === 次要按钮 === */
.btn-secondary {
  background: var(--gradient-secondary);
  color: var(--neutral-white);
  box-shadow: 0 8px 25px rgba(0, 149, 255, 0.3);
}

.btn-secondary:hover {
  box-shadow: 0 12px 35px rgba(0, 212, 255, 0.45);
}

.btn-secondary:hover > .btn-shift {
  transform: translateY(-2px);
}

/* === 按钮尺寸 === */
.btn-sm { 
  padding: var(--space-2) var(--space-4); 
  font-size: var(--text-sm);
  border-radius: 40px;
}

.btn-lg { 
  padding: var(--space-4) var(--space-8); 
  font-size: var(--text-lg);
  border-radius: 60px;
}

.btn-xl { 
  padding: 18px 48px; 
  font-size: 1.125rem;
  border-radius: 60px;
  font-weight: 600;
}