CSS Grid - Children do not center and ul does not extend full-width on transform: rotate?

I am starting with CSS and I have a doubt, I do not understand why the section . aside2, takes the width based on the text that puts it inside and not the one specified in the grid of the body, what I want to do is to have the links of. aside2 rotated but with the width assigned in the grid-template-columns and not that I take it depending on whether I add more text or not, and understand why I will not, to see if someone can help me

*fill text because it says my post is mostly code, fill text because it says my post is mostly code

*{
    margin: 0;
    padding: 0;
    list-style: none;
    text-decoration: none;
    color: white;
}
body{
    background-color: rgb(17, 17, 17);
    display: grid;
    grid-template-columns: 140px 1fr;
    grid-template-rows: 80px 1fr;
    height: 100vh;
}
aside{
    grid-column: 1/2;
    grid-row: 1/3;
    width: 100%;
    display: grid;
}
.aside1{
    background: rgb(116,191,244);
    background: linear-gradient(0deg, rgba(116,191,244,1) 0%, rgba(255,162,222,1) 100%);
    box-shadow: 30px 0px 192px 100px rgba(0,43,255,0.15);
}
.aside2{
    box-sizing: border-box;
    display:flex;
    justify-content: center;
    align-items: center;
}
.aside2 ul{
    display: flex;
    transform: rotate(-90deg);
}
.aside2 ul li{
}
.aside2 ul li a{
    color: white;
}
header{
    grid-column: 2/3;
    grid-row: 1/2;
}
main{
    grid-column: 2/3;
    grid-row: 2/3;
}
h1{
    font-size: 50px;
}

<!DOCTYPE html>
<html lang="es">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <link rel="stylesheet" href="assets/css/style.css">
</head>
<body>
    <aside>
        <section class="aside1">
            <span>Hola</span>
        </section>
        <section class="aside2">
            <ul>
                <li><a href="">Instagram</a></li>
                <li><a href="">Twitter</a></li>
                <li><a href="">Facebook</a></li>
            </ul>
        </section>
    </aside>
    <header>
        <nav>
            <a href="">G6</a>
            <ul>
                <li><a href="">Buy NFT</a></li>
                <li><a href="">Whitepaper</a></li>
                <li><a href="">Feeding</a></li>
                <li><a href="">FAQ</a></li>
                <li><a href="">Connect Wallet</a></li>
            </ul>
        </nav>
    </header>
    <main>
        <section>
            <h1>Discover rare digital art and collect NFTs</h1>
            <div>
                <img src="" alt="a">
                <img src="" alt="b">
                <img src="" alt="c">
            </div>
            <img src="" alt="FOTO NFT">
        </section>
        <div>
            <img src="" alt="Una">
            <img src="" alt="Dos">
        </div>
    </main>
</body>
</html>

Solution

A couple of things right off the get-go. You don't need to use flex-box on your grid children with align/justify-center to center them.

Simply add place-items: center; on your parent with the main grid as an alternative.

After that, just specify height and width: 100%; on your grid children so it fills the remaining space.

Moving on to aside2 taking the max-content width. You'll notice that now that each parent (aside1 & aside2) has a defined width and height, you can define a width and height on your ul which will take up the entire space vertically and horizontally if specified. Your aside2 class should look like this:

.aside2 > ul {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: space-around;
  flex-direction: column;
}

Noticed I removed the transform: rotate. You should see something like this: View Image.

Then just set your transform on the li like so:

.aside2>ul>li {
  transform: rotate(-90deg);
}

See it working here:

* {
  margin: 0;
  padding: 0;
  list-style: none;
  text-decoration: none;
  color: white;
}

body {
  background-color: rgb(17, 17, 17);
  display: grid;
  grid-template-columns: 140px 1fr;
  grid-template-rows: 80px 1fr;
  height: 100vh;
}

aside {
  grid-column: 1/2;
  grid-row: 1/3;
  width: 100%;
  display: grid;
  place-items: center;
}

.aside1 {
  background: rgb(116, 191, 244);
  background: linear-gradient(0deg, rgba(116, 191, 244, 1) 0%, rgba(255, 162, 222, 1) 100%);
  box-shadow: 30px 0px 192px 100px rgba(0, 43, 255, 0.15);
  width: 100%;
  height: 100%;
}

.aside2 {
  box-sizing: border-box;
  width: 100%;
  height: 100%;
}

.aside2 > ul {
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: space-around;
  flex-direction: column;
}

.aside2>ul>li {
  transform: rotate(-90deg);
}

.aside2 ul li a {
  color: white;
}

header {
  grid-column: 2/3;
  grid-row: 1/2;
}

main {
  grid-column: 2/3;
  grid-row: 2/3;
}

h1 {
  font-size: 50px;
}

<!DOCTYPE html>
<html lang="es">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <link rel="stylesheet" href="assets/css/style.css">
</head>

<body>
  <aside>
    <section class="aside1">
      <span>Hola</span>
    </section>
    <section class="aside2">
      <ul>
        <li><a href="">Instagram</a></li>
        <li><a href="">Twitter</a></li>
        <li><a href="">Facebook</a></li>
      </ul>
    </section>
  </aside>
  <header>
    <nav>
      <a href="">G6</a>
      <ul>
        <li><a href="">Buy NFT</a></li>
        <li><a href="">Whitepaper</a></li>
        <li><a href="">Feeding</a></li>
        <li><a href="">FAQ</a></li>
        <li><a href="">Connect Wallet</a></li>
      </ul>
    </nav>
  </header>
  <main>
    <section>
      <h1>Discover rare digital art and collect NFTs</h1>
      <div>
        <img src="" alt="a">
        <img src="" alt="b">
        <img src="" alt="c">
      </div>
      <img src="" alt="FOTO NFT">
    </section>
    <div>
      <img src="" alt="Una">
      <img src="" alt="Dos">
    </div>
  </main>
</body>

</html>