/* Vertical Rhythm Stack — 统一上下元素间距，替代手写 margin-bottom */

.stack-xs > * + * { margin-top: 8px; }
.stack-sm > * + * { margin-top: 16px; }
.stack-md > * + * { margin-top: 24px; }
.stack-lg > * + * { margin-top: 40px; }
.stack-xl > * + * { margin-top: 72px; }