How to include CSS style inside HTML style (code generated via ASP.Net MVC Razor page)

Question

I'm still at my early beginning with ASP.Net MVC. So, I'm not sure if I'm following good practices or not.

I want to generate HTML code based on CSS style

Razor page:

@foreach (p in ...)
{
    <td style="@Helper.CustomBackground(p) @Helper.CustomComplexStyle(p)">...</td>
}

CSS classes:

.complexStyleA {
   // ...
}

.complexStyleB { }

C# helper method:

// None of the styling method has the "style" attribute, so I can concatenate several custom-styles
public static class Helper
{
    // Basic direct styling
    public static string CustomBackground(object p) => "{ background: red; }";
    
    // More complex styling based on CSS ones
    public static string CustomComplexStyle(object p) => "{ // complexStyleA, complexStyleB, etc. based on p; }"
}

I don't really mind generated all the code inside the HTML tags, but generate a table with several thousand lines and can obviously reduce the file size!

Thanks for any insights :-)

UPDATE

I think that I will do something as follow :

<td @Html.Raw(@Hepers.ConcatenateCSSClasses(@CustomComplexStyle(p),
                                            @OtherCustomComplexStyle(p),
                                            ...))>
    ...
</td>

where @concatenateCSSClasses() removes all " class=" ans @...Syle(p) returns "class=\"...StyleXYZ\"", unless I can have duplicated tag attributes.. Any better ideas?

UPDATE with cleaner methods

public static string HTMLTagAttribute(FieldType fieldType, Field field = null)
{
    string output = "";

    // Makes distinction between hearder and body
    if (field == null)
    {
        output += HTMLHeaderTagClassAttributes(fieldType);
        output += HTMLHeaderTagStyleAttributes(fieldType);
    }
    else
    {
        output += HTMLBodyTagClassAttributes(fieldType, field);
        output += HTMLBodyTagStyleAttributes(fieldType, field);
    }

    return output;
}

Body only shown with clear distinction between classes and (inline styles). I don't detail the samll method HTMLWidth(), HTMLBackground(), etc. which are self explanatory.

#region HTML Body Tag Attribute Methods

private static string HTMLBodyTagStyleAttributes(FieldType fieldType, Field field)
{
    AttributeValues style = new AttributeValues("style");

    style += HTMLWidth(fieldType);
    style += HTMLBackground(fieldType, field);
    style += HTMLAlign(fieldType);

    return style.ToString();
}

private static string HTMLBodyTagClassAttributes(FieldType fieldType, Field field)
{
    AttributeValues cls = new AttributeValues("class");

    cls += HTMLTopBorder(fieldType, field);
    cls += HTMLSideBorder(fieldType);

    return cls.ToString();
}

#endregion

Class which helps concatenate class and style attribute values (with no extra space).

/// <summary>Class to help format HMTL class and style attribute values</summary>
class AttributeValues
{
    private readonly string _attribute = "";
    private readonly List<string> _values = new List<string>();

    // TODO - Make distinction bewteen class and styles        
    #region Constructors

    public AttributeValues(string attribute)
    {
        _attribute = attribute;
    }

    #endregion

    public static AttributeValues operator +(AttributeValues values, string value)
    {
        if (value != "") values._values.Add(value);

        return values;
    }
    
    public static bool operator ==(AttributeValues values, string value) => values == value;

    public static bool operator !=(AttributeValues values, string value) => values != value;
    
    #region Public Overridden Methods

    public override string ToString()
    {
        string values = "";

        foreach (string value in _values)
        {
            if (values != "") values += " ";

            values += value;
        }

        return values != "" ? $"{ _attribute }=\"{ values }\"" :"" ;
    }

    public override bool Equals(object obj) => base.Equals(obj);
    
    public override int GetHashCode() => base.GetHashCode();
    
    #endregion
}

And finally in the Razor page (apparently, I have to wrap it in HTML.Raw() because of the " (I agree that it could be refractor within the th, but doesn't make the code easier):

<td Html.Raw(Helpers.HTMLTagAttribute(Enums.FieldType.Account))>..</td>