CSS 允許應用純色作為背景，也允許使用背景圖像創建相當復雜的效果。CSS 在這方面的能力遠遠在 HTML 之上
背景色
可以使用background-color 屬性為元素設置背景色，這個屬性接受任何合法的顏色值。
這條規則把元素的背景設為灰色：p{background-color :gray;}
如果你希望背景色從元素中的文本向外至少有延伸，只需增加一些內邊框：p {background-color: gray; padding: 20px;}background-image 屬性的默認值是 none，表示背景上沒有放置任何圖像。
背景圖像
要把圖像放入背景，需要使用 background-image 屬性。
The function date_trunc is conceptually similar to the trunc function for numbers.
date_trunc('field', source)
source is a value expression of type timestamp or interval. (Values of type date and time are cast automatically, to timestamp or interval respectively.) field selects to which precision to truncate the input value. The return value is of type timestamp or interval with all fields that are less significant than the selected one set to zero (or one, for day and month).
Valid values for field are:
| microseconds |
| milliseconds |
| second |
| minute |
| hour |
| day |
| week |
| month |
| quarter |
| year |
| decade |
| century |
| millennium |
Examples:
SELECT date_trunc('hour', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-02-16 20:00:00
SELECT date_trunc('year', TIMESTAMP '2001-02-16 20:38:40');
Result: 2001-01-01 00:00:00