[css-fonts] fix typo

Author: John Daggett

css-fonts/Fonts.html

@@ -1267,7 +1267,7 @@ <h3 id=font-style-prop><span class=secno>3.4 </span>Font style: the <a
    class=property>italic</code>’ selects a font that is labeled ‘<code
    class=property>italic</code>’, or, if that is not available, one labeled
    ‘<code class=property>oblique</code>’. If no italic or oblique face is
-   available, oblique faces can by synthesized by rendering non-obliqued
+   available, oblique faces can be synthesized by rendering non-obliqued
    faces with a right sloping transformation applied. When synthesizing these
    faces, the transformation should apply to all glyphs in the same way and
    not vary based on codepoint or due to horizontal or vertical line