.tab {
    float: left;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
    width: 30%;
    height: 300px;
}

/* Style the buttons that are used to open the tab content */
.tab button {
    display: block;
    background-color: inherit;
    color: black;
    padding: 22px 16px;
    width: 100%;
    border: none;
    outline: none;
    text-align: left;
    cursor: pointer;
    transition: 0.3s;
}

/* Change background color of buttons on hover */
.tab button:hover {
    background-color: #ddd;
}

/* Create an active/current "tab button" class */
.tab button.active {
    background-color: #ccc;
}

/* Style the tab content */
.tabcontent {
    float: left;
    padding: 0px 12px;
    border: 1px solid #ccc;
    width: 70%;
    border-left: none;
    height: 300px;
}

HTML CSSResult Skip Results Iframe
EDIT ON
summary::-webkit-details-marker{display:none;}
summary::-moz-list-bullet{list-style-type:none;}
summary::marker{display:none;} 
summary {
   padding: .3em .6em .3em 1.5em;
   display:inline-block;
   font-size:1.4em;
   cursor: pointer;
   position: relative;
}
summary:before {  
  left: .3em;
  top: .4em;
  color: transparent;
  background: url("data:image/svg+xml;base64,PHN2ZyBoZWlnaHQ9IjM0IiB2aWV3Qm94PSIwIDAgMjQgMjQiIHdpZHRoPSIzNCIgeG1sbnM9Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvc3ZnIj48cGF0aCBkPSJNOC41OSAxNi4zNGw0LjU4LTQuNTktNC41OC00LjU5TDEwIDUuNzVsNiA2LTYgNnoiLz48L3N2Zz4=") no-repeat 50% 50% / 1em 1em;
  width: 1em;
  height: 1em;  
  content: "";
  position: absolute;
  transition: transform .5s;
}
details[open] > summary:before {
  transform: rotateZ(90deg);
}
summary ~ * {
   padding:0 1em 0 1em;
}
details[open] summary ~ *{ 
  animation: sweep .5s ease-in-out;
}
@keyframes sweep {
  0%    {opacity: 0;}
  100%  {opacity: 1;}
}
summary:focus {
  outline:0;
  box-shadow: inset 0 0 1px rgba(0,0,0,0.3), inset 0 0 2px rgba(0,0,0,0.3);
}
details{
  display:block;
  margin-bottom: .5rem;
}
body{background: #edf2f7;}