This style visualizes the surface and smoothness tags on highways. Currently it does the following:

• The line color primarily codes the smoothness tag, however some line coloring is done on ways according to surface, if smoothness is untagged.
• The line thickness shows you, if both tags are present.
  • thick line -> both, smoothness and surface are tagged
  • thin line -> only one of them
  • thin gray line -> none of them

• with neither surface or smoothness tag present
  • render a thin gray line of width 1.0

• with the smoothness tag present, render
  • ways with a width of 1.5
  • white solid for smoothness=excellent
  • green solid (=good) to red irregular dashed (=impassable), interpolate the rest of values
  • in zoom levels 14 and above, ways that have smoothness but lack surface are of width 1.5

• with the surface tag present, in zoom levels 14-15, introduce
  • 14] differentiation between paved-class-way/unpaved-class-ways/untagged (black/cyan/gray)
  • 15] surface values with text and use light brown for dirt|ground, light green for grass, etc..
  • ways with a width of 1.0 and the color of the text, if smoothness does not exist
  • ways with a width of 2.0-3.0 (zoom 13-15), if smoothness is present
  • line-color is _only_ derived of surface tag, if smoothness is untagged

• with the smoothness AND surface tags present, render
  • a noticable black casing and NO text (unclutters the view) if any combination of
    • smoothness=excellent|good|intermediate
    • surface=paved|asphalt

meta 
{
    title: "Surface";
    description: "Visualize surface=* of objects";
    version: "25_2019-07-18";
    author: "cmuelle8";
    
    watch-modified: true;
}

meta[lang=de]
{
    title: "Oberflächenbeschaffenheit";
    description: "Oberflächenbeschaffenheit, etwa von Wegen, hervorheben";
}

canvas
{
    background-color: #606060;
}




node
{
    symbol-shape: square;
    symbol-size: 2;
    symbol-stroke-color: #909090;
    symbol-stroke-opacity: 0.1;
}

node:connection
{
    symbol-shape: square;
    symbol-size: 2;
    symbol-stroke-color: #909090;
    symbol-stroke-opacity: 0.1;
}




way
{
    width: 1;
    color: #FF0000;
    opacity: 0.0;
}

way[landuse]:closed
{
    fill-color: yellow;
    fill-opacity: 0.02;
    z-index: -0.9;
}

way[natural]:closed
{
    fill-color: green;
    fill-opacity: 0.02;
    z-index: -0.9;
}

way[building]:closed
{
    width: 2;
    color: magenta;
    opacity: 0.1;
    fill-color: magenta;
    fill-opacity: 0.02;
    z-index: -0.8;
}

way[highway][area?]:closed
{
    width: 2;
    color: orange;
    opacity: 0.5;
    fill-color: orange;
    fill-opacity: 0.2;
    z-index: -0.5;
}




way[highway][!area]
{
    color: #909090;
    opacity: 1.0;
    z-index: 1.0;
}




way[highway][smoothness]
{
    width: 1.5;
    color: #202020;
}

way|z14-[highway][smoothness][surface]
{
    color: #909090;
}

way[highway][smoothness=impassable]
{
    color: eval(rgb((7*0.142*(1-red(prop(color)))) + red(prop(color)), (1*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(2,10,5,10);
}

way[highway][smoothness=very_horrible]
{
    color: eval(rgb((6*0.142*(1-red(prop(color)))) + red(prop(color)), (2*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(2,10,5,3);
}

way[highway][smoothness=horrible]
{
    color: eval(rgb((5*0.142*(1-red(prop(color)))) + red(prop(color)), (3*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(3,5,2,2);
}

way[highway][smoothness=very_bad]
{
    color: eval(rgb((4*0.142*(1-red(prop(color)))) + red(prop(color)), (4*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(4,4,2,2);
}

way[highway][smoothness=bad]
{
    color: eval(rgb((3*0.142*(1-red(prop(color)))) + red(prop(color)), (5*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(7,5);
}

way[highway][smoothness=intermediate]
{
    color: eval(rgb((2*0.142*(1-red(prop(color)))) + red(prop(color)), (6*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
    dashes: list(10,2);
}

way[highway][smoothness=good]
{
    color: eval(rgb((1*0.142*(1-red(prop(color)))) + red(prop(color)), (7*0.142*(1-green(prop(color)))) + green(prop(color)), blue(prop(color))));
}

way[highway][smoothness=excellent]
{
    color: white;
}




way|z13-[highway][smoothness][surface]
{
    width: 2.0;
    my-encasing: 1.0;
}

way|z14-[highway][smoothness][surface]
{
    width: 2.5;
    my-encasing: 2.5;
}

way|z15-[highway][smoothness][surface]
{
    width: 3.0;
    my-encasing: 3.0;
}




way|z14-[highway][smoothness]
{
    text: "smoothness";
    text-color: #EEE9BF;
}

way|z14-[highway][smoothness=~/excellent|good/]
{
    text: none;
    text-color: #EEE9BF;
}

way|z14-[highway][surface]
{
    font-family: Arial;
    text: "surface";
    text-color: #B0EEEE;
}

way|z14-[highway][smoothness],
way|z14-[highway][surface]
{
    font-size: 10;
    text-offset: 7;
    text-position: line;
    z-index: 1.0;
}

way|z14-[highway][surface=~/^paved|asphalt/]
{
    text-color: black;
    render-encasing: true;
    render-text: none;
}

way|z14-[highway][surface=~/paving|concrete|cobble/]
{
    text-color: #004040;
    render-encasing: true;
    render-text: eval(prop(text));
}

way|z15-[highway][surface=~/gravel|pebble/]
{
    text-color: #D0D090;
}

way|z15-[highway][surface=~/unpaved|dirt|earth|ground|mud/]
{
    text-color: #FFB0B0;
}

way|z15-[highway][surface=sand]
{
    text-color: #FFFF80;
}

way|z15-[highway][surface=grass]
{
    text-color: #80FF80;
}

way|z14-[highway][surface][!smoothness]
{
    color: eval(prop(text-color));
    dashes: list(2,1);
}

way|z14-[highway][eval(prop(render-encasing))][smoothness=~/excellent|good|intermediate/]
{
    text: eval(prop(render-text));
    casing-width: eval(prop(width) + prop(my-encasing));
    casing-color: eval(prop(text-color));
    casing-dashes: eval(prop(dashes));
}




way|z-15[highway]
{
    text: none;
}

Styles_Surface-style.mapcss, Styles_Surface.zip

If you need more styles, or have more professional needs,
give me a holler via ​http://www.openstreetmap.org/message/new/cmuelle8

sample screenshot: