Best way to dynamically change theme of my Vue.js SPA? - vue.js

Question

So I think the title is enough explaination: I would like to dynamically theme my whole application. Maybe this means to change color of all divs when I press a specific button, or change the whole webapp's colors when a specific user logs in.
Just to give some insights on what I am currently working on I will say that I have built a Vue.js app that uses many libraries, including one called Element-ui which already has a theming option built onto it. The problem is that it's written in scss and I would like to change all the variable colors during the navigation. My project looks something like this:
<template>
... some HTML and components...
</template>
<script>
... some javascript ...
</script>
<style scoped>
... some style that is scoped to the current component only ...
</style>
I have many files like this one so making a "global function" for all of them doesn't seem practical to me. Also I import the main scss file just once in my main.js.
Is there anything I can do to create a dinamic theming for my webapp? Is using saas a good idea? Javascript maybe?
EDIT
I feel like I didn't explain it good enough so I want to add a simple example. If you visit the Element page you can see in the top right corner there is a color selector that, when a color changes, it changes also the whole website's accent colors like the buttons colors, the links colors etc.
Hope this can help understanding a bit better
EDIT
Right now I have settled on a very poor and, I think, badly optimized solution. The idea is that when the user changes theme, I just create a new css file and append it to the current document.
let sheet = document.createElement('style')
sheet.innerHTML = `*[class*="--primary"]{
background-color: ${colors[0]};
}
...`;
document.body.appendChild(sheet);
I truly think this is a very bad solution but right now I can't come up with nothing else that could work dinamically when the user changes a parameter. I would really want the process to be flawless: the user picks a color and the whole application just changes to that specific color, no prebuilt theme.css.
FINAL EDIT
I've finally found a solution, refer to the answer!

Answer 1

Finally, after a few long days I came up with a solution that I think is both easy to implement and very very lightweight.
CSS VARIABLES
Before searching up a lot, I didn't even know the existance of these kind of variables and they don't seem so used. Anyway, I hope this can help someone out there seeking my same answer:
<template
<app-main></app-main>
<app-sidebar></app-sidebar>
...
</template>
<style>
:root{
--primary-color: #C5C5C5!important;
--secondary-color: #6C7478!important;
--tertiary-color: #FFFFFF!important;
--success-color: #80b855!important;
--warning-color: #eaca44!important;
--error-color: #ef4d4d!important;
}
/* Theming */
header{
background-color: var(--primary-color);
}
div{
color: var(--tetriary-colory);
}
...
/* END */
</style>
<script>
import axios from 'axios' /* all your imports etc. */
export default{
data(){
},
methods: {
axios.post(`http://localhost:8080/foo`).then(function (response){
let bodyStyles = document.body.style;
bodyStyles.setProperty('--primary-color', response.colors[0]);
bodyStyles.setProperty('--tertiary-color', response.colors[1]);
...
}
}
}
</script>
As you can see, I just initialize a few useful CSS variables and when I need them (for example in that api post call) I just modify them using a simple bodyStyles.setProperty('propertyName') function.
I really enjoy this type of setup since I use it in my login page so when a user successfully logs-in I load from the database his own colors and set them up just like that.
Hoping this can help someone! Cheers!