Sidewalks Plus JOSM Map Style, derived from https://josm.openstreetmap.de/wiki/Styles/Sidewalks with enhanced :left :right and separate support.

SideWalksPlus.mapcss

meta {
        title: "Sidewalks Plus";
        description: "Visualizes the sidewalk attribute of highways. sidewalk=* is rendered as a thick dashed line, separately mapped sidewalks tagged footway=sidewalk are rendered thicker.";
        link: "https://wiki.openstreetmap.org/wiki/Key:sidewalk";
        author: "Cobra;Aharvey";
        version: "0.7_2021-06-28";
        min-josm-version: "4399";
}

meta[lang=de] {
        title: "Gehwege";
        description: "Visualisiert Gehweg-Attribute von Straßen. sidewalk=* wird als gestrichelte dicke Linie gerendert, separat gemappte Gehwege mit footway=sidewalk werden dicker gerendert.";
}

way[sidewalk=right]::sidewalks_right,
way[sidewalk:right=separate]::sidewalks_right,
way[sidewalk:right=yes]::sidewalks_right {
        width: 3;
        dashes: 5, 1;
}
way[sidewalk=left]::sidewalks_left,
way[sidewalk:left=separate]::sidewalks_left,
way[sidewalk:left=yes]::sidewalks_left {
        width: 3;
        dashes: 5, 1;
}
way[sidewalk=separate]::sidewalks_right,
way[sidewalk=both]::sidewalks_right,
way[sidewalk=no]::sidewalks_right,
way[sidewalk:right=no]::sidewalks_right {
        width: 3;
        dashes: 5, 1;
}
way[sidewalk=separate]::sidewalks_left,
way[sidewalk=both]::sidewalks_left,
way[sidewalk=no]::sidewalks_left,
way[sidewalk:left=no]::sidewalks_left {
        width: 3;
        dashes: 5, 1;
}

way[sidewalk=right]::sidewalks_right,
way[sidewalk:right=separate]::sidewalks_right,
way[sidewalk:right=yes]::sidewalks_right,
way[sidewalk=both]::sidewalks_right,
way[sidewalk=separate]::sidewalks_right,
way[sidewalk=no]::sidewalks_right,
way[sidewalk:right=no]::sidewalks_right {
        offset: eval(0 - 10 - (prop("width") * 0.5) - (prop("width", "default") * 0.5));
}

way[sidewalk=left]::sidewalks_left,
way[sidewalk:left=separate]::sidewalks_left,
way[sidewalk:left=yes]::sidewalks_left,
way[sidewalk=both]::sidewalks_left,
way[sidewalk=separate]::sidewalks_left,
way[sidewalk=no]::sidewalks_left,
way[sidewalk:left=no]::sidewalks_left {
        offset: eval(10 + (prop("width") * 0.5) + (prop("width", "default") * 0.5));
}

way[sidewalk=right]::sidewalks_right,
way[sidewalk:right=yes]::sidewalks_right,
way[sidewalk=left]::sidewalks_left,
way[sidewalk:left=yes]::sidewalks_left {
        color: #00ff00;
}
way[sidewalk=both]::sidewalks_right {
        color: #00ff00;
}
way[sidewalk=both]::sidewalks_left {
        color: #00ff00;
}

way[sidewalk:right=no]::sidewalks_right,
way[sidewalk=no]::sidewalks_right {
        color: #ff0000;
        opacity: 0.5;
}
way[sidewalk:left=no]::sidewalks_left,
way[sidewalk=no]::sidewalks_left {
        color: #ff0000;
        opacity: 0.5;
}

way[sidewalk:left=separate]::sidewalks_left,
way[sidewalk:right=separate]::sidewalks_right {
        color: #00ff00;
        opacity: 0.5;
}
way[sidewalk=separate]::sidewalks_right {
        color: #00ff00;
        opacity: 0.5;
}
way[sidewalk=separate]::sidewalks_left {
        color: #00ff00;
        opacity: 0.5;
}

way[footway=sidewalk] {
        width: 3;
}