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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

            
              <div style="font-size: 16px">Test 16px (Min)</div>
<div id="test">Test <span id="size"></span></div>
<div style="font-size: 24px">Test 24px (Max)</div>

<div id="vw" style="position: absolute; top: 0; right: 0;"></div>

<p>Author : <a href="http://neo.s21.xrea.com/">Neo</a></p>
            
          
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CSS

            
              /// 引数に単位が付いている場合は単位を除去して数値のみ返却する
/// 
/// @param $num {number} 数値のみ返却してほしい値
/// @return {number} 引数を数値のみに変換した値
@function strip-unit($num) {
  @if type-of($num) == 'number' and not unitless($num) {
    @return $num / ($num * 0 + 1);
  }
  
  @return $num;
}

/// 単位がない数値に px を付ける
/// 
/// @param $num {number} 単位のみの値
/// @return {number} 引数を px 単位に変換した値
@function to-px($num) {
  @return $num * 1px;
}

/// レスポンシブルにフォントサイズを変更する
/// 
/// @param {number} $min-font-size 最小フォントサイズ (px)
/// @param {number} $max-font-size 最大フォントサイズ (px)
/// @param {number} $min-breakpoint 最小ビューポート幅 (px)
/// @param {number} $max-breakpoint 最大ビューポート幅 (px)
/// @param {number} $root-font-size ルートのフォントサイズ・未指定時は 16 (px)
@mixin responsive-font-size($min-font-size, $max-font-size, $min-breakpoint, $max-breakpoint, $root-font-size: 16px) {
  $min-font-size-num : strip-unit($min-font-size);
  $max-font-size-num : strip-unit($max-font-size);
  $min-breakpoint-num: strip-unit($min-breakpoint);
  $max-breakpoint-num: strip-unit($max-breakpoint);
  $root-font-size-num: strip-unit($root-font-size);
  
  // Min Font Size
  font-size: to-px($min-font-size-num);
  
  // Responsive Font Size
  @media (min-width: to-px($min-breakpoint-num)) {
    $min-font-size-rem        : ($min-font-size-num / $root-font-size-num * 1rem);
    $min-breakpoint-percent-px: ($min-breakpoint-num / 100 * 1px);
    $font-size-difference     : ($max-font-size-num - $min-font-size-num);
    $breakpoint-difference    : ($max-breakpoint-num - $min-breakpoint-num);
    $differences              : (100 * $font-size-difference / $breakpoint-difference);
    
    font-size: calc( #{$min-font-size-rem} + ( 1vw - #{$min-breakpoint-percent-px} ) * #{$differences} );
  }
  
  // Max Font Size
  @media (min-width: to-px($max-breakpoint-num)) {
    font-size: to-px($max-font-size-num);
  }
}



// 16px @ 768px から 24px @ 1024px に変更する (ルートのフォントサイズは未指定で 16px として扱わせる)
html {
  @include responsive-font-size(16px, 24px, 768px, 1024px);
}
            
          
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JS

            
              /** フォントサイズとビューポート幅を出力する */
function detectSizes() {
  const test = document.getElementById('test');
  const size = document.getElementById('size');
  const vw   = document.getElementById('vw');
  
  size.innerHTML = window.getComputedStyle(test).fontSize;
  vw.innerHTML   = window.innerWidth + 'px';
}

document.addEventListener('DOMContentLoaded', detectSizes);
document.addEventListener('resize', detectSizes);
            
          
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999px

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