G145: Fix link (#4577)

Co-authored-by: Patrick H. Lauke <[email protected]>
Co-authored-by: Mike Gower <[email protected]>

Author: 3 people

techniques/general/G145.html

@@ -7,7 +7,7 @@
             that is presented over a background. This technique relaxes the 4.5:1
             contrast ratio requirement for text that is at least 18 point (if not bold) or at least 14 point (if bold).</p>
       <div class="note">
-        <p>When evaluating this success criterion, the font size in points should be obtained from the user agent or calculated on font metrics in the way that user agents do. Point sizes are based on the CSS pt size <a href="">CSS3 Values</a>. The ratio between sizes in points and CSS pixels is 1pt = 1.333px, therefore 14pt and 18pt are equivalent to approximately 18.5px and 24px.</p>
+        <p>When evaluating this success criterion, the font size in points should be obtained from the user agent or calculated on font metrics in the way that user agents do. Point sizes are based on the CSS pt size <a href="https://www.w3.org/TR/css3-values/#absolute-lengths">CSS3 Values</a>. The ratio between sizes in points and CSS pixels is 1pt = 1.333px, therefore 14pt and 18pt are equivalent to approximately 18.5px and 24px.</p>
       </div>
       <p>If the background is a solid color (or all black or all white) then the
             contrast ratio of the larger-scale text can be maintained by making sure that each