Свойство flex

flex-element {
	flex: 1;
	/* аналогично */
	flex-grow: 1;
}

flex-element {
	flex: 1 200px;
	/* аналогично */
	flex-grow: 1;
	flex-basis: 200px;
}

flex-element {
	flex: 1 2 200px;
	/* аналогично */
	flex-grow: 1;
	flex-basis: 200px;
	flex-shrink: 2;
}