img.ctf_logo {
  /* from black icon to light grey */
  filter=> invert(0.8) sepia(1) saturate(0) hue-rotate(0deg);
}

.challenge-button{

}
.corner-button-check{
  margin-right: 3px !important;
}
.challenges-row{
  display: inline-block;
}
.category-challenges {
  display: inline-block;
  width: auto;
  max-width: 450px;
  border: 5px;
  border-style: solid;
  border-color: #ddd;
  border-radius: 7px;
  padding: 5px;
  margin: 5px;
  background: linear-gradient(whitesmoke, white);
}
.category-challenges:hover {
  border-color: #aaa;
}

.category-challenges::after{
  height: 5px;
  width: 40px;
  background-color: #ddd;
  content: "  ";
  position: absolute;
  bottom: -10px;
  left: calc(50% - 20px);
  margin-left: -5px;
}
.pt-5{
  display: inline-block;
}
.col-md-3{
  width: auto;
  padding-right: 5px;
  padding-left: 5px;
  max-width: 450px !important;
  vertical-align: bottom;
}
h3{
  font-size: 1rem;
}
.jumbotron {
  margin-left: -100%;
  margin-right: -100%;
}