flexbox library code example

Example 1: flexbox grid

.container {
    max-width: 1335px;
    margin: 0 auto;
}
.grid-row {
    display: flex;
    flex-flow: row wrap;
    justify-content: flex-start;
}
.grid-item {
    height: 550px; /*optional*/
    flex-basis: 20%; /* initial percantage */
    -ms-flex: auto;
    width: 259px; /*optional*/
    position: relative;
    padding: 10px; /*optional*/
    box-sizing: border-box;
}
@media(max-width: 1333px) {/*xl*/
	.grid-item {
    	flex-basis: 33.33%;
    }
}
@media(max-width: 1073px) {/*lg*/
    .grid-item {
    	flex-basis: 33.33%;
    }
}
@media(max-width: 815px) {/*md*/
	.grid-item {
    	flex-basis: 50%;
    }
}
@media(max-width: 555px) {/*sm*/
	.grid-item {
    	flex-basis: 100%;
    }
}

Example 2: flexbox css

.container {
  align-content: flex-start | flex-end | center | space-between | space-around | space-evenly | stretch | start | end | baseline | first baseline | last baseline + ... safe | unsafe;
}

Example 3: flexbox

Display: flex 
Flex-direction: row | row-reverse | column | column-reverse
align-self: flex-start | flex-end | center | baseline | stretch
justify-content: start |  center | space-between | space-around | space-evenly

Example 4: flexbox css

.container {
  flex-flow: column wrap;
}

Example 5: flexbox css

.container {
  justify-content: flex-start | flex-end | center | space-between | space-around | space-evenly | start | end | left | right ... + safe | unsafe;
}

Example 6: flexbox

Please read flexbox & grid in CSS TRIX, 
make hands-on project watching (WESBOS videos - it's really useful)
also try [FLEXBOX - froggy] and [GRID - garden] games