Flexbox Froggy solutions (levels 1 to 24) - https://flexboxfroggy.com/

flexbox-froggy.css

/* Level 1 */

#pond {
  display: flex;
  justify-content: flex-end;
}

/* Level 2 */

#pond {
  display: flex;
  justify-content: center;
}

/* Level 3 */

#pond {
  display: flex;
  justify-content: space-around;
}

/* Level 4 */

#pond {
  display: flex;
  justify-content: space-between;
}

/* Level 5 */

#pond {
  display: flex;
  align-items: flex-end;
}

/* Level 6 */

#pond {
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Level 7 */

#pond {
  display: flex;
  align-items: flex-end;
  justify-content: space-around;
}

/* Level 8 */

#pond {
  display: flex;
  flex-direction: row-reverse;
}

/* Level 9 */

#pond {
  display: flex;
  flex-direction: column;
}

/* Level 10 */

#pond {
  display: flex;
  flex-direction: row-reverse;
  justify-content: flex-end;
}

/* Level 11 */

#pond {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}

/* Level 12 */

#pond {
  display: flex;
  flex-direction: column-reverse;
  justify-content: space-between;
}

/* Level 13 */

#pond {
  display: flex;
  align-items: flex-end;
  justify-content: center;
  flex-direction: row-reverse;
}

/* Level 14 */

#pond {
  display: flex;
}

.yellow {
  order: 1;
}

/* Level 15 */

#pond {
  display: flex;
}

.red {
  order: -1;
}

/* Level 16 */

#pond {
  display: flex;
  align-items: flex-start;
}

.yellow {
  align-self: flex-end;
}

/* Level 17 */

#pond {
  display: flex;
  align-items: flex-start;
}

.yellow {
  order: 1;
  align-self: flex-end;
}

/* Level 18 */

#pond {
  display: flex;
  flex-wrap: wrap;
}

/* Level 19 */

#pond {
  display: flex;
  flex-wrap: wrap;
  flex-direction: column;
}

/* Level 20 */

#pond {
  display: flex;
  flex-flow: column wrap;
}

/* Level 21 */

#pond {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-start;
}

/* Level 22 */

#pond {
  display: flex;
  flex-wrap: wrap;
  align-content: flex-end;
}

/* Level 23 */

#pond {
  display: flex;
  flex-wrap: wrap;
  align-content: center;
  flex-direction: column-reverse;
}

/* Level 24 */

#pond {
  display: flex;
  flex-flow: column-reverse wrap-reverse;
  justify-content: center;
  align-content: space-between;
}