<!DOCTYPE html>
<style>
.test {
  width: 200px;
  overflow: hidden;
}

.float {
  float: left;
  width: 50%;
  height: 100px;

  background: orange;
  clip-path: polygon(0 0, 100% 100%, 0 100%);
}

.flex {
  display: flex;
  height: 50px;
  background: rebeccapurple;
}
</style>
<div class="test">
  <div class="float"></div>
  <div class="flex"></div>
</div>
