Access color string from code behind in .css-File in ASP

I have 3 files for my Login-Screen: Login.aspx, Login.aspx.cs, LoginStyle.css

On the Page_Load method I am recieving some data from the current system among other things the theme-color as string (e.g #003b67).

In my .css-File i have defind 3 style rules, which should use this color.

.linkButtonPassword:hover {
        color: #38d39f;
}

.login-input-div.focus > .login-faItem > i {
    color: #38d39f;
}

.login-input-div:before, .login-input-div:after {
    content: '';
    position: absolute;
    bottom: -2px;
    width: 0%;
    height: 2px;
    background-color: #38d39f;
    transition: .4s;
}

so my question is, is there a way to replace the current color-string “#38d39f” with my color from code behind without defining the style in my .aspx-File? (is there a way to access a kind of variable in my css-file)

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Answers:

Method 1

Part 1:

Part 2:

Answers:

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Method 1

CSS files aren’t processed by ASP.NET (unless you reconfigure your entire HTTP pipeline, which is a bad idea in general), so the short answer is “no”.

…however a solution exists with CSS Custom Properties!

Part 1:

In your .aspx page, ideally in the <head> (you’re using <asp:ContentPlaceHolder, I hope?), put this after your current <link rel="stlyesheet"> element:

<style type="text/css">
:root {
    --theme-color: <%= this.customColor %>;
}

.linkButtonPassword:hover,
.login-input-div.focus > .login-faItem > i,
.login-input-div:before,
.login-input-div:after {
    color: var(--theme-color);
}
</style>

You could argue this is the same thing as overwriting the properties with <%= %> directly – but the difference here is that you can now remove the color: property from the above and use color: var(--theme-color); directly in your .css file!

Part 2:

So now your <head> should contain this:

<style type="text/css">
:root {
    --theme-color: <%= this.customColor %>;
}
</style>

And your .css file should contain this:

.linkButtonPassword:hover {
    color: #38d39f;
    color: var(--theme-color);
}

.login-input-div.focus > .login-faItem > i {
    color: #38d39f;
    color: var(--theme-color);
}

.login-input-div:before,
.login-input-div:after {
    content: '';
    position: absolute;
    bottom: -2px;
    width: 0%;
    height: 2px;
    background-color: #38d39f;
    background-color: var(--theme-color);
    transition: .4s;
}

The color values are repeated twice (first as a literal hex-color, then again with var(--theme-color)) to ensure backwards compatibility with older browsers that don’t support CSS Custom Properties (i.e. IE11 – which I assume you have to support seeming as you’re using ASP.NET WebForms).

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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