Material Fonts and Sizes for fman + HiDPI fix. Version 3. Includes the SCSS source file with all my notes and the resulting CSS file for use in fman. Note: I did not update the source scss file yet.

_Theme.scss

////////////////////////////////////
// Material Typeface Rules for fman
////////////////////////////////////

// This is written for Qt5 / fman.

// Why? While I really like the color scheme I'm just more used to a larger font size which meant I had a hard time reading what fman is showing me.
// I also noticed some problems which going from a "standard" display to a high DPI display in a multi monitor setup. 
// I don't think this will slove the problem yet but that's how everything started.

/* Notes and Research */

// According to the Qt5 documentation qcss is quite limited in what it can do in terms of styling. 
// For example font-size only supports px and pt instead of also supporting "rem" or "em", but it seems fman will only accept "pt" anyways.

// Some key units that I found online
// ------------------------
//     - 1 px = 0.75 point
//     - 1pt is 1.333333px :(
//     - 1rem = 16px in a 96dpi web browser
//     - 1 google unit = 0.0625rem
// ------------------------

// NOTE: letter-spacing is unfortunately not supported (yet?). Could be maybe exposed via the QFont class...

// NOTE: This written for 96dpi what I assume most users use these days. It really depends on the screen size and resolution.
// If you are one of the happy user that owns a high DPI display you might have to tweak the formula. 
// A good start is how your browser understands "1rem" in high DPI mode expressed in "px".

// Reference: https://material.io/design/typography/the-type-system.html
// The base CSS file I copied from the Core Plugin: https://github.com/fman-users/Core/blob/master/Theme.css

// In case you need a 'Licence' have a look here: https://creativecommons.org/publicdomain/zero/1.0/deed.de (CC0 1.0 also known as Public Domain in some places)
// NOTE: The licence only applys to the modifications I made. The original Theme.css is untouched by this!

// Lastly even though you don't need to if you are more experienced in design and or sass I would be more than happy 
// if you contribute advice or changes back to me so everyone can benefit from them.



/*********************************/
/* == SCSS magic starts here === */
/*********************************/

// The workhorse function for this stylesheet.
//
// All base units and numbers are defined here and the main formula.
// $size is a number without suffix and represents what I call "Google units"
// This function will return your google units as fman compatible pt
//
// For more infomation lookup the type scale table here: https://material.io/design/typography/the-type-system.html#type-scale
@function gtype-scale($size) {
    $groot-unit: 0.0625; //rem
    $unit-rem: 16; //px
    $px-unit: 0.75pt;
    // Qt doesn't like floating point pts
    @return floor(($size * $groot-unit) * $unit-rem * $px-unit);
}

// Some precalculated numbers for different type scale levels. 
// If you look at the type scale table you will notice that not every scale level is implemented. 
// This is intentional but feel free to add the scales that you need.
$scale-body1: gtype-scale(16);
$scale-body2: gtype-scale(14);
$scale-subtitle1: gtype-scale(16);
$scale-subtitle2: gtype-scale(14);
$scale-caption: gtype-scale(12);
$scale-heading5: gtype-scale(24);
$scale-heading6: gtype-scale(20);
$medium-font: 500; // 500 = Medium weight. Not supported by Noto Sans.
$regular-font: normal;

// All levels are compsed as mixins for easier handling
// ... it is a system after all
@mixin body1 {
    font-size: $scale-body1;
    font-weight: $regular-font;
}

@mixin subtitle2 {
    font-size: $scale-subtitle2;
    font-weight: $medium-font;
}

@mixin caption {
    font-size: $scale-caption;
    font-weight: $regular-font;
}

@mixin heading5 {
    font-size: $scale-heading5;
    font-weight: $regular-font;
}

@mixin heading6 {
    font-size: $scale-heading6;
    font-weight: $medium-font;
}

/***************************************/
/* == fman style rules start here === */
/*************************************/

* {
    
    font-family: Roboto, Noto Sans, Segoe UI, Ubuntu, sans-serif;
    @include body1;
}

th {
    vertical-align: center;
    @include subtitle2;
}

.statusbar {
    padding: 4px;
    @include body1;
}

.quicksearch-query, .quicksearch-item-title {
    @include heading6;
}

.quicksearch-item {
    padding-top: 1px;
    padding-left: 4px;
    padding-right: 4px;
    border-top: 1px solid #4d4d4d;
    border-bottom: 1px solid #363636;
    @include heading5;
}

.quicksearch-item-title {
    color: #c8c8c8;
    
}

.quicksearch-item-title-highlight {
    color: white;
}

.quicksearch-item-hint {
    color: white;
}

.quicksearch-item-description {
    color: #8f908a;
}

Theme.css

* {
    font-family: Roboto, Noto Sans, Segoe UI, Ubuntu, sans-serif;
    font-size: 12pt;
    font-weight: normal;
  }
  
  th {
    vertical-align: center;
    font-size: 10pt;
    padding-top: 8px;
    height: 24px;
  }
  
  .statusbar {
    padding: 3px;
    font-size: 10pt;
    font-weight: normal;
  }
  
  .quicksearch-query, .quicksearch-item-title {
    font-size: 15pt;
    font-weight: 500;
  }
  
  .quicksearch-item {
    padding-top: 1px;
    padding-left: 4px;
    padding-right: 4px;
    border-top: 1px solid #4d4d4d;
    border-bottom: 1px solid #363636;
    font-size: 18pt;
    font-weight: normal;
  }
  
  .quicksearch-item-title {
    color: #c8c8c8;
  }
  
  .quicksearch-item-title-highlight {
    color: white;
  }
  
  .quicksearch-item-hint {
    color: white;
  }
  
  .quicksearch-item-description {
    color: #8f908a;
  }