动效能让人停一下。
看一眼，然后留下来。

/*
 * Masked Word Flip
 *
 * A two-line label whose words roll up
 * out of a mask, replaced by the next
 * pair, with dots showing which is up.
 *
 * How it moves
 * - Each line is a one-cell grid with
 *   overflow: hidden.
 * - The word up sits at translateY(0),
 *   the others wait below, at 100%.
 * - A flip moves the current word
 *   0 -> -100%, the next 100% -> 0,
 *   cubic-bezier(.22,1,.36,1).
 *
 * Do not change (the feel breaks)
 * - Out-expo: fast start, long settle.
 * - Both words move together by 100%.
 */