chart: highlight only hovered line, dim others on hover

Author: guenhter

index.html

@@ -604,6 +604,7 @@ <h3>Alternative indexes</h3>
     <li><a href="https://www.tiobe.com/tiobe-index/" target="_blank" rel="noopener">TIOBE Index</a> — search-engine-based language popularity index</li>
     <li><a href="https://pypl.github.io/PYPL.html" target="_blank" rel="noopener">PYPL Index</a> — popularity of programming languages by tutorial searches</li>
     <li><a href="https://redmonk.com/sogrady/category/programming-languages/" target="_blank" rel="noopener">RedMonk Rankings</a> — language rankings combining GitHub and Stack Overflow data</li>
+    <li><a href="https://githut.info/" target="_blank" rel="noopener">GitHut</a> — interactive visualization of programming language activity on GitHub</li>
   </ul>
 </footer>
 
@@ -746,7 +747,8 @@ <h3>Alternative indexes</h3>
     smooth: true,
     symbol: 'none',
     lineStyle: { width: 1.5 },
-    emphasis: { lineStyle: { width: 3 } },
+    emphasis: { focus: 'self', lineStyle: { width: 3 } },
+    blur: { lineStyle: { opacity: 0.15 } },
     data: months.map(m => {
       const v = byMonth.get(m)?.get(lang);
       return v != null ? +v.toFixed(2) : null;
@@ -774,6 +776,8 @@ <h3>Alternative indexes</h3>
     grid,
     tooltip: {
       trigger: 'axis',
+      axisPointer: { type: 'line' },
+      triggerEmphasis: false,
       backgroundColor: '#1c2128',
       borderColor: '#30363d',
       textStyle: { color: '#e6edf3', fontSize: 12 },