max-width=XXX (thieets lap de hien thi dung tren cac cua so nho - sao cho không có horizontal bar - thanh trượt ngang)

The max-width property is used to set the maximum width of an element.
The max-width can be specified in length values, like px, cm, etc., or in percent (%) of the containing block, or set to none (this is default. Means that there is no maximum width).
The problem with the <div> above occurs when the browser window is smaller than the width of the element (500px). The browser then adds a horizontal scrollbar to the page.
Using max-width instead, in this situation, will improve the browser's handling of small windows.
Tip: Drag the browser window to smaller than 500px wide, to see the difference between the two divs!

This element has a height of 100 pixels and a max-width of 500 pixels.

Note: The value of the max-width property overrides width.
The following example shows a <div> element with a height of 100 pixels and a max-width of 500 pixels:

Example

div {
    max-width: 500px;
    height: 100px;
    background-color: powderblue;}