PX和PT转换的公式：
pt=px乘以3/4。
比如12px×3/4=9pt大小。
PX和em转换的公式：
em=16乘以px，也就是说1.5em=1.5×16=24px。
设计中常用PX/EM/PT/百分比转换表格
| Pixels | EMs | Percent | Points |
|---|---|---|---|
| 6px | 0.375em | 37.50% | 5pt |
| 7px | 0.438em | 43.80% | 5pt |
| 8px | 0.5em | 50% | 6pt |
| 9px | 0.563em | 56.30% | 7pt |
| 10px | 0.625em | 62.50% | 8pt |
| 11px | 0.688em | 68.80% | 8pt |
| 12px | 0.75em | 75% | 9pt |
| 13px | 0.813em | 81.30% | 10pt |
| 14px | 0.875em | 87.50% | 11pt |
| 15px | 0.938em | 93.80% | 11pt |
