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

• show highways that neither have surface=* or smoothness=* as dotted black

• with the smoothness tag render a
  • white solid for smoothness=excellent
  • then move from green (=good) to red (=impassable) for the rest of smoothness values and use dashed stiles as smoothness values
  • ways that have smoothness but lack surface are of width 1.5

• with the surface tag render
  • ways with a width of 3.0
  • a noticable black casing for values paved|asphalt|concrete|concrete_pavers
  • for the rest render the value with text and text-color (light brown for dirt, ground, mud, light green for grass, etc..)
  • ways that have surface but not smoothness are rendered solid gray at width 3.0

• do not render text for the most common values (excellent, good, asphalt, paved) as they are easily identifyable by color code and would distract from the "problem zones"

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: white;
    symbol-stroke-opacity: 0.1;
}

node:connection
{
    symbol-shape: square;
    symbol-size: 2;
    symbol-stroke-color: white;
    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]
{
    opacity: 1.0;
    z-index: 1.0;
}



way[highway][!surface][!smoothness]
{
    color: #202020;
    dashes: list(2,1);
}

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

way[highway][surface]
{
    color: #909090;
    width: 3;
}

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[highway][surface],
way[highway][smoothness]
{
    print-text: true;
    text-color: #B0E0EE;
    text-offset: 5;
}

way[highway][surface=grass]
{
    text-color: #B0FFB0;
}

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

way[highway][surface=~/.*gravel.*|pebble.*/]
{
    text-color: #FFFFB0;
}

way[highway][surface=~/paved.*|asphalt.*|concrete.*|cobble.*/][smoothness=~/excellent|good|intermediate|bad/]
{
    print-text: false;
    casing-width: +3;
    casing-color: black;
    casing-dashes: eval(prop(dashes));
}

way[highway][smoothness=excellent],
way[highway][smoothness=good]
{
    print-text: false;
}

way[highway][smoothness][eval(prop(print-text))]
{
    font-size: 10;
    text: "smoothness";
    text-color: #EEE9BF;
    text-position: line;
    z-index: 1.0;
}

way[highway][surface][eval(prop(print-text))]
{
    font-size: 10;
    font-family: Arial;
    text: "surface";
    text-position: line;
    z-index: 1.0;
}

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: