diff --git a/2-ui/3-event-details/8-onscroll/1-endless-page/solution.md b/2-ui/3-event-details/8-onscroll/1-endless-page/solution.md
@@ -1,16 +1,16 @@
-The core of the solution is a function that adds more dates to the page (or loads more stuff in real-life) while we're at the page end.

-We can call it immediately and add as a `window.onscroll` handler.

-The most important question is: "How do we detect that the page is scrolled to bottom?"

-Let's use window-relative coordinates.

-The document is represented (and contained) within `<html>` tag, that is `document.documentElement`.

-We can get window-relative coordinates of the whole document as `document.documentElement.getBoundingClientRect()`, the `bottom` property will be window-relative coordinate of the document bottom.

-For instance, if the height of the whole HTML document is `2000px`, then:

```js
// when we're on the top of the page
@@ -22,7 +22,7 @@ document.documentElement.getBoundingClientRect().top = 0
document.documentElement.getBoundingClientRect().bottom = 2000
```

-If we scroll `500px` below, then:

```js
// document top is above the window 500px
@@ -31,8 +31,7 @@ document.documentElement.getBoundingClientRect().top = -500
document.documentElement.getBoundingClientRect().bottom = 1500
```

-When we scroll till the end, assuming that the window height is `600px`:
-

```js
// document top is above the window 1400px
@@ -41,13 +40,13 @@ document.documentElement.getBoundingClientRect().top = -1400
document.documentElement.getBoundingClientRect().bottom = 600
```

-Please note that the `bottom` can't be `0`, because it never reaches the window top. The lowest limit of the `bottom` coordinate is the window height (we assumed it to be `600`), we can't scroll it any more up.

-We can obtain the window height as `document.documentElement.clientHeight`.

-For our task, we need to know when the document bottom is not no more than `100px` away from it (that is: `600-700px`, if the height is `600`).

-So here's the function:

```js
function populate() {

diff --git a/2-ui/3-event-details/8-onscroll/1-endless-page/task.md b/2-ui/3-event-details/8-onscroll/1-endless-page/task.md
@@ -2,19 +2,20 @@ importance: 5

---

-# Endless page

-Create an endless page. When a visitor scrolls it to the end, it auto-appends current date-time to the text (so that a visitor can scroll more).

-Like this:

[iframe src="solution" height=200]

-Please note two important features of the scroll:

-1. **The scroll is "elastic".** We can scroll a little beyond the document start or end in some browsers/devices (empty space below is shown, and then the document will automatically "bounces back" to normal).
-2. **The scroll is imprecise.** When we scroll to page end, then we may be in fact like 0-50px away from the real document bottom.

-So, "scrolling to the end" should mean that the visitor is no more than 100px away from the document end.

-P.S. In real life we may want to show "more messages" or "more goods".
diff --git a/2-ui/3-event-details/8-onscroll/2-updown-button/task.md b/2-ui/3-event-details/8-onscroll/2-updown-button/task.md
@@ -2,15 +2,15 @@ importance: 5

---

-# Up/down button

-Create a "to the top" button to help with page scrolling.

-It should work like this:
-- While the page is not scrolled down at least for the window height -- it's invisible.
-- When the page is scrolled down more than the window height -- there appears an "upwards" arrow in the left-top corner. If the page is scrolled back, it disappears.
-- When the arrow is clicked, the page scrolls to the top.

-Like this (top-left corner, scroll to see):

[iframe border="1" height="200" link src="solution"]