CSS Requirements

Question

what I have so far I need help with seperading the style sheet into three files:
/styles/colors.css
/styles/formatting.css
/styles/transitions-animations.css

and anythe else I may have missed

<!DOCTYPE html>
<html>

<body>

<main>

<nav>
<a href="index.html">Home</a>
<a href="contact.html">Contact</a>
<a href="about.html">About</a>
</nav>
<h1>Welcome to my (about me) site</h1>
<picture>
<source media="(min-width:650px)" srcset="./images/me3-650.jpg">
<source media="(min-width:465px)" srcset="./images/me3-465.jpg">
<img src="./images/me3.JPG" alt="ME" style="width:auto;">
</picture>

<h3>HI there this is one of my favorite songs down below.</h3>
<iframe width="420" height="345"
src="https://www.bing.com/search?q=Nirvana%20-%20The%20Man%20Who%20Sold%20The %20World&pc=0TTE&ptag=C1N2A04173C0C08&form=CONBNT&conlogo=CT3210127&shtp=GetUrl&shid=38702244-8c35-477e-a042- 805b2b2d81bc&shtk=TmlydmFuYSAtIFRoZSBNYW4gV2hvIFNvbGQgVGhlIFdvcmxkIChNVFYgVW5wbHVnZ2VkKQ%3D %3D&shdk=UkVNQVNURVJFRCBJTiBIRCEgVGFrZW4gZnJvbSB0aGUgMjV0aCBBbm5pdmVyc2FyeSBFZGl0aW9ucyBvZiBOaXJ2YW5hIGI%3D&shhk=7xVtP%2FaZHQw%2B31lGYV%2F3cJukwLOZgUcFMDTYwdmuLsA %3D&shth=OVP.2ZxeDKLNemtX7dQ99X3ETQHgFo">

</iframe>
<footer>
<div class="foot">
<p>Author: Josiah McSweeney<br>
<p>Copyright Reserved</p>
</div>
</footer>
</main>
</body>

</html>

style.css:

*{
margin: 0;
padding: 0;
}
@media (min-width:1224px){
body{
background-color: darkblue;
color: white;
}
main{
display: grid;
grid-template-areas: "nav"
"h1"
"picture"
"h3"
"iframe"
"footer";
grid-template-columns: auto;
grid-template-rows: auto;
}
nav{
display: flex;
flex-direction: row;
justify-content: end;
background-color: lightcoral;
}

picture{
text-align: center;
}
nav>a{
padding: 10px;
margin: 10px;
}
main>h1, h3{
text-align: center;
}
iframe{
margin: auto;
}
footer{
position: fixed;
left: 0;
bottom: 0;
width: 100%;
background-color:antiquewhite;
color: black;
}
footer>.foot{
padding: 10px;
display: flex;

flex-direction: row;
justify-content: space-evenly;
}
.foot:nth-of-type(1) {
flex-shrink: 1;
}
.foot:nth-of-type(2) {
flex-grow: 1;
}
}

@media (min-width:726px){
body{
background-color: darkblue;
color: white;
}
main{
display: grid;
grid-template-areas: "nav"
"h1"
"picture"
"h3"
"iframe"
"footer";
grid-template-columns: auto;
grid-template-rows: auto;
}

nav{
display: flex;
flex-direction: row;
justify-content: end;
background-color: lightcoral;
}
picture{
text-align: center;
}
nav>a{
padding: 10px;
margin: 10px;
}
main>h1, h3{
text-align: center;
}
iframe{
margin: auto;
}
footer{
position: fixed;
left: 0;
bottom: 0;
width: 100%;
background-color:antiquewhite;
color: black;
}
footer>.foot{
padding: 10px;
display: flex;
flex-direction: row;
justify-content: space-evenly;
}

.foot:nth-of-type(1) {
flex-grow: 1;
}
.foot:nth-of-type(2) {
flex-shrink: 1;
}
}

@media (min-width:320px) and (max-width:726px){
body{
background-color: darkblue;
color: white;
}
main{
display: grid;
grid-template-areas: "nav"
"h1"
"picture"
"h3"
"iframe"
"footer";
grid-template-columns: auto;
grid-template-rows: auto;
}
nav{

display: flex;
flex-direction: row;
justify-content: center;
background-color: lightcoral;
}
picture{
text-align: center;
}
nav>a{
padding: 10px;
margin: 10px;
}
main>h1, h3{
font-size: 16px;
text-align: center;
}
iframe{
margin: auto;
width: 300px;
}
footer{
position: fixed;
left: 0;
bottom: 0;
width: 100%;
background-color:antiquewhite;
color: black;
}