Parent DIV : RED
Child DIV : YELLOW

I NEED FULL WIDTH CHILD TO STICK TO THE BOTTOM

Parent DIV : Available width, fixed height
Child DIV : Fixed width, fixed height, (extended : absolute positioning, bottom:0%)

WORKS

Parent DIV : Available width, fixed height
Child DIV : Available width, fixed height, (extended : absolute positioning, bottom:0%)

FAILS, CHILD MOVES OUTSIDE PARENT

Parent DIV : Available width, fixed height
Child DIV : Fixed width of 100%, fixed height, (extended : absolute positioning, bottom:0%)

WORKS