```
{% endtab %}
{% tab title="index.css" %}
```css
body {
background-color: #2c3e50;
color: #34495e;
}
.btn {
cursor: pointer;
}
.clicked {
color: #7f8c8d;
}
.form,
.greetings {
display: none;
}
.showing {
display: block;
}
@keyframes fadeIn {
from {
opacity: 0;
}
to {
opacity: 1;
}
}
.bgImage {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: -1;
animation: fadeIn 0.5s linear;
}
```
{% endtab %}
{% tab title="bg.js" %}
```javascript
const body = document.querySelector("body");
const IMG_NUMBER = 6;
function paintImage(imgNumber){
const image = new Image();
image.src = `images/${imgNumber + 1}.jpg`;
image.classList.add("bgImage");
body.prepend(image);
}
function genRandom(){
const number = Math.floor(Math.random() * IMG_NUMBER);
return number;
}
function init(){
const randomNumber = genRandom();
paintImage(randomNumber);
}
init();
```
{% endtab %}
{% endtabs %}
{% hint style="info" %}
**math** : 수학에서 자주 사용하는 **상수와 함수**들을 **미리 구현**해 놓은 자바스크립트 표준 **내장 객체**
* **math.ceil :** 소수점을 올림
* **math.floor** : 소수점을 내림
{% endhint %}
---
# Agent Instructions: Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.
Perform an HTTP GET request on the current page URL with the `ask` query parameter:
```
GET https://westsilver.gitbook.io/study-script/nomad-script/vanillajs/momentum/image-background.md?ask=
```
The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.
Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.