index.css

* {
  margin: 0;
  padding: 0;
}

html,
body,
#mask {
  width: 100%;
  height: 100%;
}

#mask {
  background-color: #c9c9c9;
  position: relative;
}

#mask .center {
  position: absolute;
  background-color: #fff;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  padding: 10px;
}
#mask .center .title {
  position: absolute;
  display: flex;
  align-items: center;
  height: 56px;
  top: -61px;
  left: 0;
  padding: 5px;
  padding-left: 10px;
  padding-bottom: 0;
  color: rgba(175, 47, 47, 0.8);
  font-size: 26px;
  font-weight: normal;
  background-color: white;
  padding-right: 50px;
  z-index: 2;
}
#mask .center .title img {
  height: 40px;
  margin-right: 10px;
}

#mask .center .title::before {
  content: "";
  position: absolute;
  width: 0;
  height: 0;
  border: 65px solid;
  border-color: transparent transparent white;
  top: -65px;
  right: -65px;
  z-index: 1;
}

#mask .center > img {
  display: block;
  width: 700px;
  height: 458px;
}

#mask .center a {
  text-decoration: none;
  width: 45px;
  height: 100px;
  position: absolute;
  top: 179px;
  vertical-align: middle;
  opacity: 0.5;
}
#mask .center a :hover {
  opacity: 0.8;
}

#mask .center .left {
  left: 15px;
  text-align: left;
  padding-right: 10px;
  border-top-right-radius: 10px;
  border-bottom-right-radius: 10px;
}

#mask .center .right {
  right: 15px;
  text-align: right;
  padding-left: 10px;
  border-top-left-radius: 10px;
  border-bottom-left-radius: 10px;
}