windowsとmacで違いの出にくいフォント指定を目指します。
A:
font-family:"Hiragino Kaku Gothic Pro","ヒラギノ角ゴ Pro W3","ＭＳ ゴシック",Helvetica,Arial,sans-serif;
あいうえおＡＢＣ１２３ABC123
012345789abcdefghijklmnOPQRSTUVWXYZ
B:
font-family:Helvetica,Arial,sans-serif,"Hiragino Kaku Gothic Pro","ヒラギノ角ゴ Pro W3","ＭＳ ゴシック";
あいうえおＡＢＣ１２３ABC123
012345789abcdefghijklmnOPQRSTUVWXYZ
C:
全角に font-family:"Hiragino Kaku Gothic Pro","ヒラギノ角ゴ Pro W3","ＭＳ ゴシック";
半角に font-family:Helvetica,Arial,sans-serif;
あいうえおＡＢＣ１２３ABC123
012345789abcdefghijklmnOPQRSTUVWXYZ