Inappropriate CAPPEDWORD conversion from PascalCase to snake_case

[hillin]

Json:

{
    CSSColor: "#FFFFFF"
}

Rust:

#[derive(Deserialize)]
#[serde(rename_all = "PascalCase")]
struct Data {
    // css_color: String,  // does not work, expects field "CssColor" in json
    c_s_s_color: String,   // works but ugly
}