* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Arial;
  outline: none;
}
body {
  height: 100vh;
  display: grid;
  place-items: center;
  background: #eef3f9;
}
/* by Qasim Sarawri */
.box {
  width: 320px;
  padding: 20px;
  background: #fff;
  border-radius: 5px;
  border: 2px solid #95b2c2;
  padding-top: 30px;
  padding-bottom: 15px;
  box-shadow: 5px 5px 10px rgba(0,0,0,0.2);
  overflow: hidden;
}
.box #input {
  width: 100%;
  height: 80px;
  text-align: right;
  padding: 10px;
  border: 2px solid #95b2c2;
  border-radius: 3px;
  font-size: 20px;
  background: #eef3f9;
}
.box .btns {
  width: 100%;
  height: 45px;
  margin: 8px 0;
  display: flex;
  justify-content: space-between;
  align-items: center;
  user-select: none;
}
.box .btns span {
  height: 100%;
  display: grid;
  place-items: center;
  border-radius: 3px;
  color: #000;
  border: 2px solid #95b2c2;
  font-weight: bold;
  font-size: 20px;
  box-shadow: 0 2px 3px rgba(0,0,0,0.2);
}
.box .btns span:active {
  background: #333;
  color: #fff;
}
.box .btns #ac {
  background: #000;
  color: #fff;
  width: 50px;
}
.box .btns #del {
  width: 50px;
  height: 100%;
}
.box .btns #char {
  width: 50px;
  height: 100%;
}
.box .btns .num {
  width: 50px;
  height: 100%;
}
.btns #plus {
  width: 106px;
  height: 100%;
  background: #197;
  color: #fff;
  border-color: #fff;
}
.btns #eval {
  width: 106px;
  background: #1876f3;
  color: #fff;
  border-color: #fff;
}