Changing back ground colour for dyslexia

Hi there,
Could anyone please help , Im dysleix and would like to use remnote for my work .the only thing is i need a blue back ground. I have no coding background but have got as far as finding a CSS code and i think we add it as a snippet in the Custom CSS screen. But i don’t know how to apply it? I’ve found a blue colour to use and this is the text i have.
.rem-reference{
background-color: #b0e0e6;
color: unset;
text-decoration: underline;
text-transform: lowercase;

}
Any help very welcome.

try this
#document {
background-color: blue
}
.navigation-bar {
background-color: blue;
}
#document .document-title {
background-color: transparent;
color:white;
}
body {
background-color: blue;
}
.rem-text {
color: white;
}

Follow the picture to apply it