the html container with d-flex is called flex item code example

Example 1: ustify-content: flex-end; bootstrap

<div class="d-flex justify-content-end">...</div>

Example 2: css flex property

flex: none                                            /* value 'none' case */
flex: <'flex-grow'>                                   /* One value syntax, variation 1 */
flex: <'flex-basis'>                                  /* One value syntax, variation 2 */
flex: <'flex-grow'> <'flex-basis'>                    /* Two values syntax, variation 1 */
flex: <'flex-grow'> <'flex-shrink'>                   /* Two values syntax, variation 2 */
flex: <'flex-grow'> <'flex-shrink'> <'flex-basis'>    /* Three values syntax */
flex: inherit