associate form controls to labels (#186)

Author: estelle

tools/color-mixer/index.html

@@ -134,15 +134,15 @@ <h3>Color mixer</h3>
       <label id="mix-output-text"></label>
 
       <div>
-        <label id="percentage-one-label">50%</label>
+        <label id="percentage-one-label" for="percentage-one">50%</label>
         <input id="percentage-one" type="range" name="percent1" step="0.1" />
       </div>
       <div>
-        <label id="percentage-two-label">50%</label>
+        <label id="percentage-two-label" for="percentage-two">50%</label>
         <input id="percentage-two" type="range" name="percent2" step="0.1" />
       </div>
 
-      <label>color space: </label>
+      <label for="color-space">color space: </label>
       <select id="color-space">
         <option value="srgb">srgb</option>
         <option value="srgb-linear">srgb-linear</option>
@@ -157,7 +157,7 @@ <h3>Color mixer</h3>
         <option value="oklch">oklch</option>
       </select>
 
-      <label id="interpolation-method-label">interpolation method: </label>
+      <label id="interpolation-method-label" for="interpolation-method">interpolation method: </label>
       <select id="interpolation-method">
         <option value="shorter hue" selected>shorter hue</option>
         <option value="longer hue">longer hue</option>